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New Coros Dura 2 Solar features ultra-modern design and huge battery life, but it's the smaller bevel I love
Hands-on with the sharp-looking new bike computer from Coros
Michigan bet big on EV batteries. Here’s what happened.
Four years after Michigan pledged more than $1 billion in incentives to build an electric vehicle battery industry, the state has clawed back millions of dollars after companies have drastically changed their plans.
Josh Jacobs returns to Packers practice
Jacobs spoke to the media for the first time Wednesday since an altercation with his then-girlfriend in the spring. He was charged with battery and criminal damage to property after domestic abuse allegations.
Forge Nano to Trade on NASDAQ as NANO After Completing Business Combination with Archimedes Tech SPAC Partners II Co.
Forge Nano common stock and warrants expected to begin trading on NASDAQ on October 22, 2026 under the symbols “NANO” and “NANOW,” respectivelyPublic listing positions Forge Nano to accelerate growth across semiconductor manufacturing equipment and advanced battery technologies DENVER, Oct. 21, 2026 (GLOBE NEWSWIRE) -- Forge Nano, Inc., a leading U.S.-based semiconductor equipment and advanced materials company pioneering Atomic Layer Deposition (“ALD”) technology for artificial intelligence (“A
Green Science Alliance opens Swiss battery recycling lab
The Japanese chemical and greentech firm has opened a battery recycling laboratory at the Switzerland Innovation Park Biel/Bienne (SIPBB) in the canton of
Huawei-backed smart car business to cooperate with CATL on battery swapping
BEIJING, Oct 19 (Reuters) - Huawei-affiliated Chinese smart vehicle company Yinwang Intelligent Technology has signed a cooperation agreement with CATL and CATL's battery-swapping subsidiary, it said on Monday. The collaboration between Yinw...
Here’s how iPhone Duo’s battery capacity compares to other iPhones
After pre-orders for iPhone Duo opened, Apple uploaded an EU regulatory document that finally revealed the true battery capacity for...
Teardown of revised Switch 2 console confirms lack of anticipated upgrade
Nintendo’s updated EU console was an opportunity to debut a leaked screen. Yet a teardown of the handheld with a modified Switch 2 battery compartment didn't reveal the Sharp LCD display. The current system suffers from poor pixel response times, leading to ghosting in games.
Apple Reveals iPhone Duo's Battery Capacity
Apple on Friday published an EU energy label for the iPhone Duo that reveals the device has a total battery capacity of 4,883 mAh. The document appears to confirm a previous leak that showed the iPhone Duo has 2,962 mAh and 1,921 mAh battery cells totaling 4,883 mAh. iPhone Duo is an eSIM-only device, so this battery capacity figure should apply worldwide, as there is no version of the device with a physical SIM card tray that would have a slightly smaller battery.
Red Magic 12 Pro+ gaming phone launches with Snapdragon 8 Elite Extreme Gen 6, liquid-cooling system, 8,400mAh battery, and more
Red Magic 12 Pro+ launches in China with a 185Hz OLED display, Snapdragon 8 Elite Extreme Gen 6, an 8,400mAh battery and active cooling.
Battery-free smart glasses monitor your health using blink energy
Your eyes blink roughly 14 to 20 times a minute, and every one of those movements is wasted energy. Engineers at Northwestern University have found a way to put that motion energy to work, powering a pair of battery-free health-sensing glasses.
New batch of Zelda 40th Switch 2 console and Pro Controller contain replaceable battery
UK video game and toy retailer Smyths have just received a new batch of stock of the Zelda 40th anniversary Nintendo Switch 2 console and the Zelda 40th anniversary Pro Controller and these new…
Amwins unveils battery, EV coverage
Amwins Global Risks said Tuesday it has expanded its specialist commercial and industrial insurance facility to cover battery energy storage systems and electric vehicle infrastructure.
iPhone Duo: Apple Charging $49 for New Cover Layer, $229 for Battery
We just published Apple's list of iPhone Duo repair fees for customers without AppleCare+ coverage, and we want to bring extra attention to two of the fees in particular: a new cover layer costs $49, and a replacement battery is $229. Apple's vice president of hardware engineering Kate Bergeron revealed that the iPhone Duo's nano-texture cover layer above the inner display can be removed and replaced.
iPhone Duo: Skipping AppleCare+ Could Be $1,499 Mistake
Apple today listed its estimated repair fees for the iPhone Duo without AppleCare+ coverage, with the maximum fee in the U.S. for "other damage" set at $1,499. If you only damage certain parts of the iPhone Duo, the fees are more manageable. For example, the repair fee for damaged back glass is set at $199. If you eventually want to replace the battery in your iPhone Duo, that will cost you $229.
Redwood Materials pitches AI data centers on off-grid battery power
JB Straubel's Redwood Materials is using retired EV batteries to help AI data centers get electricity faster, without waiting for the strained grid.
Ray-Ban Meta Audio glasses review: No camera, no problem
Normal-looking glasses with solid audio and way better battery life is a win for everyone.
Samsung’s first Android XR glasses leak in 25 styles alongside 9-hour battery, specs [Gallery]
Samsung’s first Android XR glasses are right around the corner and, ahead of launch, another leak reveals every style you’ll...
CNET's iPhone 18 Pro and Pro Max’s Battery Tests Show Surprising Results
Turns out the new iPhone 18 Pro and Pro Max have more to offer than just their fancy camera and new burgundy color. Both performed well in our battery tests.
Google's Sleek New Fitbit Edge Is Packed With Health Features And A Replaceable Battery
The Fitbit Edge will be in stores starting October 27 for $179.99.
iPhone 18 Pro vs iPhone 17 Pro: Is the Upgrade Worth It?
iPhone 18 Pro vs iPhone 17 Pro: Check the camera, display, design, battery, charging, price and other one-on-one specs comparison here.
Apple A20 outclasses Android rivals in our review: iPhone's lead is impressive
New iPhone 18 Pro reviewed! Our review shows what the flagship can do: a 2nm A20 Pro processor, 12 GB of RAM and a 6.3" ProMotion OLED display. Find out all about the camera upgrade (48 MP with a variable aperture), the long-lasting 4,056 mAh battery and faster 45-watt charging
ALDS Game 5, White Sox vs Guardians Chat and Discussion
Yay, more playoff baseball. Here is your Battery Power ALDS Game 5 Chat and Discussion. However, you’re not limited to this. It’s also for whatever. There are some football games going on as well. I’m losing weight to the tune of 10 pounds in 4 weeks. My kid just discovered Teenage Mutant Ninja Turtles. It’s […]
South Korean 'robot dog' became first to run a marathon on a single battery charge
A quadruped robot scampered more than 26.2 miles of uneven, hilly terrain alongside human runners without needing to be recharged.
Dell launches Nvidia RTX Spark laptop with 18-core CPU, 3.2K 120Hz OLED display and 99 Wh battery
Dell has launched its first XPS laptop powered by Nvidia’s RTX Spark platform. The XPS 16 combines an 18-core N1X chip, 5,120 GPU cores, 32 GB of unified memory and a 16-inch 3.2K Tandem OLED touchscreen.
Images: Science Square's latest jobs hub arrives on Westside
One of the world’s leading battery makers officially cut the ribbon this week on a $56-million, jobs-producing investment into research and development at the cusp of Georgia Tech.Spread across four stories where English Avenue meets Midtown, Duracell’s Global Innovation Center for Research and Development marks a key addition for Science Square, an 18-acre, mixed-use district expected to produce 500 homes, retail, and nearly 2 million square feet of lab and office space across multiple phases.
Ring's first smart lock can be hand-cranked when its battery dies
Amazon-owned Ring is entering the smart lock market with a device designed to tackle a common concern: getting locked out when the battery dies
Ring’s first smart lock can be charged by turning a dial when the battery unexpectedly dies
A few turns of the dial will generate enough power to unlock your door.
Garmin's New Smartwatch Has Battery Life That Laps the Apple Watch Ultra 4
The Garmin Enduro 4 promises up to 320 hours of battery while still offering the health and fitness tracking features of the Fenix 9 Pro.
Three Years of 80% Charge Limits on iPhone: The Results
Since 2023, Apple's newer iPhones have had an 80 percent charge limit for those who want to extend battery lifespan. Charging to 80 percent instead of 100 percent is supposed to put less stress on the battery, improving longevity. For the last three years, I've used that setting on my iPhone. I started with the iPhone 15 Pro Max, then did the iPhone 16 Pro Max, and most recently, the iPhone 17 Pro Max.
iPhone 13 Pro vs. iPhone 18 Pro Buyer's Guide: Is It Worth Upgrading?
Apple released the iPhone 18 Pro and iPhone 18 Pro Max in September 2026, five years after the iPhone 13 Pro and iPhone 13 Pro Max. The 2021 models introduced ProMotion displays, macro photography, a 3x Telephoto camera, and substantially longer battery life than their predecessors. They remain capable phones and support iOS 27, but owners now have five generations of upgrades to consider.
Samsung Galaxy S27 Ultra: (Slightly) faster charging and potentially fewer camera artifacts
While industry insiders are currently focused on the starting mass production of some Galaxy S27 series components like the Exynos 2700, leakers are sharing more details about battery and camera improvements that could matter to end users.
iPhone Owners Turn Off This Setting To Save Battery Life
The Background App Refresh on iPhone keeps your apps updated with the latest information before they are opened, which is nice, but it drains the battery.
Rapper Rick Ross arrested on domestic violence battery charge
Rick Ross has been arrested in Miami on two counts of felony battery, including one by strangulation, which allegedly involve domestic violence. The "Hustlin'" rapper, 50, was arrested around 5
Rapper Rick Ross charged with battery after domestic violence accusation
MIAMI BEACH, Fla. — Rapper Rick Ross was arrested in Miami Beach early Thursday and charged with battery related to a domestic violence accusation, authorities said.
Rapper Rick Ross charged with battery after domestic violence accusation
Authorities say rapper Rick Ross was arrested early Thursday in Miami Beach and charged with battery related to a domestic violence accusation. Online court records show Ross, whose legal name
Rapper Rick Ross charged with battery after domestic violence accusation
Authorities say rapper Rick Ross was arrested early Thursday in Miami Beach and charged with battery related to a domestic violence accusation. Online court records show Ross, whose legal name
Toyota opens $50M+ EV battery lab at its R&D center near Ann Arbor
Toyota opened a new electric vehicle battery lab in Saline Township despite the national pullback from electrification.
Rapper Rick Ross charged with battery after domestic violence accusation
Authorities say rapper Rick Ross was arrested early Thursday in Miami Beach and charged with battery related to a domestic violence accusation. Online court records show Ross, whose legal name
Rapper Rick Ross charged with battery after domestic violence accusation
Authorities say rapper Rick Ross was arrested early Thursday in Miami Beach and charged with battery related to a domestic violence accusation. Online court records show Ross, whose legal name
Rapper Rick Ross charged with battery after domestic violence accusation
Authorities say rapper Rick Ross was arrested early Thursday in Miami Beach and charged with battery related to a domestic violence accusation. Online court records show Ross, whose legal name
Rapper Rick Ross arrested on domestic violence strangulation charge
Rick Ross has been arrested in Miami on two counts of felony battery, including one by strangulation, which allegedly involve domestic violence. The "Hustlin'" rapper, 50, was arrested around 6
vivo X Fold6 finally goes global
Most of its specs are intact too, and the battery capacity is cut by only a tiny amount, believe it or not. Exactly three months after being released in...
Samsung’s Galaxy SmartTag 3 works with iPhones, but not Android Find Hub
Samsung has announced its Galaxy SmartTag 3 as a new AirTag rival with an updated design, longer battery life, and...
Apple Watch Ultra 4 Review: Still the Best Health Buddy for Your Wrist
The fourth-gen Apple Watch Ultra doesn't reinvent the wheel, but it sure does pack plenty of upgrades, like more accurate health tracking and longer battery life.
Motorola’s wide Razr looks small, chunky, and powerful in detailed new leaks
Motorola’s Razr Wide Fold could pack a 165Hz display, 5,000mAh battery, and dual 50MP cameras in a compact design.
Green Science Alliance Developed Stable Rechargeable Aqueous Aluminum Ion Battery with Conductive Carbon Rubber Sheet as Cathode Current Collector
/PRNewswire/ -- In modern society, rechargeable batteries, particularly lithium-ion batteries (LIBs), have become the most practical option for energy storage...
Battery Power Braves End of Season Top 30 Prospects
Caminiti reclaims his spot at the top of our rankings with an absolutely stellar 2026
Honor’s Magic 9 Pro Max has a big camera and a bigger battery
The phone borrows Arri’s “three-lens turret” design.
Honor Magic 9 Pro Max debuts with stylish design, dual 200MP camera, 8800mAh battery
It’s September 28, and Honor debuts the Magic 9 Pro Max with a stylish design and a mesmerizing upgrade over the previous-generation handset. From name and appearance to internal specifications, the company has given a complete makeover to its annual flagship. It’s time to explore the top-tier smartphone. Magic 9 Pro Max debuts as the […]
NIO Stock Jumps Overnight As $2.4B Nio Power Deal Brings Geely Into Its Battery Swap Business
The companies are also discussing wider use of battery swapping across Geely-related vehicles, though plans remain preliminary.
Solar, Wind, Battery Storage, And Politics - It's Complicated
Clean energy is a no-brainer. Why is it so hard to accomplish?
Sennheiser Momentum 5 review: Great sound, incredible battery life, and few compromises
I spent the last few weeks with the Sennheiser Momentum 5 to determine if this pair actually stands out, testing everything from sound quality and noise cancellation to comfort and battery life.
iPhone 18 Pro Max Vs. Pixel 11 Pro XL: Which Flagship Should You Buy?
We traveled with the iPhone 18 Pro Max and Pixel 11 Pro XL and compared the things you rely on every day, from battery life to cameras.
You can check your Samsung Galaxy's health with a built-in test
Bluetooth, sensors, speakers and battery life are just a few of the things you can check by running Samsung's health test on your S26 or earlier model Galaxy.
REM sleep paradox: Dreaming may drain the brain’s energy even as fuel supply rises
Scientists discovered a surprising energy paradox in the brain during REM sleep, the stage most closely associated with dreaming. Blood supply to the brain begins increasing even before REM starts, but neurons’ immediately available energy, measured as ATP, then drops. The finding suggests that dreaming may require such intense internal processing that neurons consume energy faster than it can be replenished.
Review: The iPhone 18 Pro is Apple's coolest smartphone (but only literally)
Better thermals and battery life make this iterative update nicer to use.
Leeds United extend official partnership with NOCO
Leeds United are delighted to announce an extension to the club’s official partnership with global leader in battery power solutions, NOCO.As part of the continued partnership, the NOCO brand will f...
Former sports medicine director accused of sexually abusing more than a dozen college athletes
A grand jury indicted Robert Murphy on nine counts of sexual contact under pretext of medical treatment and 23 counts of sexual battery.
Former sports medicine director accused of sexually abusing more than a dozen college athletes
A grand jury indicted Robert Murphy on nine counts of sexual contact under pretext of medical treatment and 23 counts of sexual battery.
Apple Watch Ultra 2 vs. Ultra 4 Buyer's Guide: Should You Upgrade?
The Apple Watch Ultra 4 arrives three years after the Ultra 2. Across those two generations, Apple added satellite connectivity, a larger display, new health sensors, and longer battery life. Are those changes enough to justify replacing an Ultra 2 or paying more for the newest model? Both watches retain a 49mm titanium case, an Action button, a siren, a 3,000-nit display, dual-frequency GPS, and support for recreational diving to 40 meters. The Apple Watch Ultra 4 starts at $799 in the U.S.
The Beats 360 are essentially true wireless earbuds disguised as headphones.
As confirmed by Beats product manager Jeff Bruksch, the new Beats 360 headphones use a true wireless architecture with each earcup containing its own battery, antenna, and processing components. It allows Beats to “significantly reduce the cabling between the two sides,” according to Bruksch. > Because we don’t have the traditional system including a charging case, we have a cable for power supply and power management between the left and right sides so that you don’t have to charge both sides and the left and right sides power on/off together. Having a cable for power management only explains the lack of audio support through the USB-C.
iPhone 18 Pro Review: The Best Camera Smartphone Of 2026
As expected, the iPhone 18 Pro and iPhone 18 Pro Max are iterative upgrades, but the camera quality and battery life are best in class for 2026.
Apple Releases watchOS 27.0.1 With Fix for Restart Bug
Apple today released watchOS 27.0.1, a minor update to the watchOS 27 operating system that came out last week. The update is limited to the Apple Watch Series 12 and Apple Watch Ultra 4. watchOS 27.0.1 can be downloaded through the Settings app on the watch or the Apple Watch app on a connected iPhone. Software can only be installed when the Apple Watch is on the charger and has over 50 percent battery.
Galaxy Tab S12+ and S12 Ultra specs leak - here's what will be upgraded
As we've seen before, both slates will be powered by the Dimensity 9500. The "plus" model is getting a new battery too, but it loses a camera.
Scientists Built a Paper-Based Battery You Can Swallow. It Could Power Medical Pills for Days
The tiny battery could help doctors track treatment and deliver medicine.
Xiaomi 18 Pro series goes official with ‘privacy screen,’ 8,500 mAh battery, and Snapdragon 8 Elite Extreme Gen 6
Xiaomi has just launched its new Xiaomi 18 Pro and Xiaomi 18 Pro Max in China with flagship specs, massive...
These discreet hearing aid glasses now have better voice boosting and battery life
A subtle alternative for those not wanting to wear hearing aids.
Amazfit T-Rex Dual Solar Hands-On: AMOLED meets Solar?!?
Does solar actually make sense on an AMOLED display? I dig into the real-world battery details to find out!
Battery Size Upgrades Inbound for Galaxy S27 Ultra and Pro
Batteries for the upcoming Galaxy S27 Ultra and Galaxy S27 Pro are going through regulatory approvals, and thanks to that, we’re getting an idea for how big Samsung is going for 2027. Things are looking good for Samsung fans. For the Galaxy S27 Ultra, which is the flagship lineup’s flagship device, the size is shown...
Scientists made a paper battery you can swallow to power internal medical devices
A paper-based, ingestible battery powered medical devices inside pigs for up to three days before gradually breaking down, a new study reported.
iPhone 14 Pro vs. iPhone 18 Pro Buyer's Guide: Should You Upgrade?
Apple announced the iPhone 18 Pro and iPhone 18 Pro Max earlier this month, arriving four years after the iPhone 14 Pro and iPhone 14 Pro Max. Four generations of changes make for a substantial upgrade, bringing larger displays, an all-new design, improvements to every camera, significantly longer battery life, faster charging, USB-C connectivity, and support for Apple Intelligence.
Already-operating battery storage projects are key to making the business case for the next assets bankable
Existing assets provide crucial benchmarks for sizing and other crucial battery storage design decisions, writes Ashutosh Vats at 3E.
Strain-reduced battery electrode design accommodates multiple ions
Avoiding lattice distortion in multivalent batteries enables the harmonious storage of both calcium and magnesium ions.
iFixit Shares iPhone 18 Pro Teardown With Inside Look at New Features
iFixit today published an iPhone 18 Pro and iPhone 18 Pro Max teardown in both article and video formats, providing a closer look inside the new devices. The teardown confirms the battery capacities for the eSIM-only models: iPhone 18 Pro: 4,288 mAh (+0.8% vs. 4,252 mAh for iPhone 17 Pro) iPhone 18 Pro Max: 5,567 mAh (+9.4% vs.
Huawei Pura X View hands-on reveals unusually wide smartphone
Huawei’s Pura X View pairs an unusually wide 16:9.5 OLED display with strong cameras, a 7,000 mAh battery and a design praised for comfortable typing, reading, video and gaming. However, importing the smartphone may not be ideal due to uncertain global software optimization and app compatibility.
The iPhone 18 Pro Max ships to you with a smaller battery than advertised. But it's okay
Your iPhone 18 Pro Max has a new battery feature that limits the capacity. Here's what you need to know.
iOS 27 Battery Drain & Overheating? Here’s How to Fix It
Fix iOS 27 battery drain and overheating by identifying power-hungry background processes. Check your battery usage by app to stop the excessive drain today.
Galaxy S27 Pro and S27 Ultra reportedly getting major battery upgrade
Samsung’s Galaxy S27 Ultra and S27 Pro are expected to get major battery upgrades, with certification records pointing to typical capacities of about 5,700mAh and 5,200mAh, respectively. This would mark the most significant battery upgrade since the S20.
Here's how Apple circumvented the battery shipping restrictions for iPhone 18 Pro Max
Learn about this simple software trick that regulators hate. If you've been following the smartphone trends in recent years, you've probably noticed that...
The Big Holes in Wearable Heart Rate Variability And Readiness Scores
On September 9th, Apple announced it was revamping its Apple Watch Health Sensing System, rolling out a Readiness score (0 to 10), and increasing the frequency of heart rate variability (HRV) outputs 24-fold. This can be viewed as upping its competition with various other consumer wearable sensors. These “readiness scores” as a composite of multiple metrics, with heart rate variability (HRV) being front and center for most. The majority of Americans are now using wearable sensors, which equates to well over 100 million adults. HRV and Readiness scores are increasingly being marketed as a measurement of autonomic nervous system health, a digital marker for future disease, a clock for biological age, and a holistic metric to promote healthspan and even longevity. (Apple also introduced a new longevity tab and “Health Age”.) None of this has been proven. In this edition of Ground Truths I am going to review what we know about heart rate variability and readiness scores. Heart Rate Variability HRV is the variation in normal heart cycle timing. The variability of the heart rate, the barely perceptible millisecond changes in time between consecutive heart beats (see R-R intervals in the Figure below, left panel), is due to interplay between the sympathetic and parasympathetic (vagal nerve) inputs. Distinct from heart rate, individuals with the same heart rate can have very different HRVs. It is a rough reflection of the autonomic nervous system (ANS) activity, inadequate to say whether a person’s ANS function is abnormal. For more than three decades, heart rate variability (HRV) has been measured and several studies have found an association of low HRV and clinical outcomes, particularly a link with higher all-cause and cardiovascular mortality. There have also been less well established links of low HRV to risk of early cognitive impairment, dementia, mental illness, Type 2 diabetes and substance abuse. An important reminder is that HRV is a surrogate marker without any established cause-and-effect relationship. If you increase your HRV, that doesn’t mean it will improve health outcomes. In fact, there is no hard evidence for that. All that work linking to health outcomes was done with electrocardiogram (ECG) derived HRV. Now, in the era of consumer wearables, this is getting assessed differently, by optical pulse (yes, the lights you see) plethysmography (PPG) or what is called pulse rate variability (PRV). They are not the same, as shown below (right panel) and only concordant when the delay between the ECG and pulse is kept constant, which basically means at rest. I should mention there’s also what I will call MPV, a mattress mechanical movement sensor, a derived heart rate variability, that companies like Eight Sleep use, even further away from directly measuring HRV. HRV has not one uniform measurement but many different types of quantification, such as RMSSD, the magnitude of difference between successive R-R intervals of normal sinus beats (N-N) or SDNN, the standard deviation of NN intervals, both in milliseconds. SDNN is one of the so-called frequency domain HRVs (others are LF, HF, LF/HF). Different wearable sensors use different metics; Apple has relied on SDNN and nearly all of the others use RMSSD, which is generally considered the more accurate metric. There’s also the different length of time measured, such as for a matter of minutes, all day, or an overnight’s sleep. Short measurements are especially problematic since they don’t capture enough of respiratory modulation and other factors that influence HRV. Share Ground Truths How well does HRV correlate with PRV? There are very limited studies, especially independently done. One that is commonly cited was conducted by Air Force researchers in only 13 healthy adults assessing Oura ring 3 and 4, Whoop 4.0, and Garmin Fenix 6 and showed a correlation coefficient of 0.88 to 0.97 and a mean absolute percentage error from 6 to 10%. The correlation is not a perfect 1.0, but there’s at least a fairly high level of correlation. HRV is supposed to increase during the night due to takeover of the parasympathetic nervous system, and higher during deep sleep. A recent example of my 1 week, all day “HRV,” and one during sleep is shown below. As you can see, the N of 1 data are inconsistent for the same days from different sensors (Oura, AppleWatch, Fitbit Air, and Eight Sleep) by patterns, absolute numbers, and comparison with prior days and weeks. The largest study in over 8 million Fitbit users (the old version, not Google Fitbit Air, introduced in May 2026) gives you a sense of the effect of age, sex, and the 2 different main HRV (here PRV) metrics, with RMSSD on the left and SDRR (=SDNN) on the right below. That study, from data collected in 2018, is a major outlier, since all the more recent ones are tiny with respect to sample size. Many of the companies have not had independent evaluation of their HRV, such as Eight Sleep, but have published a low standard error on their website. There are some other published studies on the correlation between HRV and PRV, but they are all small and only in healthy adults. A scoping review emphasized the lack of study in underrepresented individuals, including the aged, people of color (which affects the PPG signal), and individuals who are underweight or obese. Add the typical adult age 60 plus with one or more chronic diseases. For example, one study in over 900 adults found poor correlation of HRV and PRV, non-uniformly underestimated across many chronic diseases (cardiovascular, endocrine, neurological, respiratory, and others), concluding PRV is “an invalid surrogate for HRV.” A recent systematic review of 43 studies comparing HRV and PRV found reasonable pooled absolute standardized error (HRV as gold standard) but only 10 of the studies provided quantitative synthesis in ideal conditions. Their main conclusion was similarly cautious: “PPG-derived HRV [PRV] should not be regarded as universally interchangeable with ECG-derived HRV across all devices, populations, and recording contexts.” Factors Affecting HRV and PRV That gets me to the long list of factors that affect HRV (and PRV) besides the device, the type of measurement (RMSSD, SDNN or others), the person’s signal, the sensor site, the duration of data capture, if weighting by sleep stage is used, how artifact is processed and corrected. And this list is not complete!: Oura puts out data from their community of users (who input data) on what affects their overnight HRV. The factors currently provided are: no alcohol (increase 8%), melatonin (increase 2%, float tank (increase 2%), wine (decrease 4%), and party (decrease 14%) in overnight HRV. Must be some big parties! Subscribe What is a PRV measurement good for? It has been falsely characterized as an index of “autonomic balance” and a specific indicator of stress. A 2018 review of the studies available for HRV and its relationship to stress, not using any of the current wearables, found that stress can lower HRV. But so can many other factors. The non-specificity of the signal, indexed to the table above, is striking. Evidence from a UK Biobank study of over 46,000 participants with actual HRV looked at genetically predicted HRV, a genetic risk score, that failed to show the expected HRV-mortality link, indicating that _HRV is likely not causa_l, but rather a reflection of person’s physiologic state. A review of consumer wearable HRV data from 5 longitudinal studies showed that nighttime PRV was not associated with perceived stress, and surprisingly higher HRV, in the largest cohort (N=717 participants), was correlated with higher stress. An Oura ring cohort of 525 first-year college students found a link between overnight PRV and perceived stress, but that was also seen with resting heart rate, sleep, and respiratory rate. Several very small studies have examined the relationship of HRV and athletic injuries or guiding training with mixed, and predominantly negative results. HRV biofeedback training with paced breathing had no significant effect on reducing stress or raising HRV, as demonstrated with sham controlled trials. When HRV for multiple days showed a decline in conjunction with body temperature, the Oura ring published data for prediction of Covid. The WHOOP company sponsored an observational study, published in 2026, of 30,000 users for 72 weeks, without a control group, that reported reduced alcohol intake (5.8 % points) by self-report. That doesn’t tell us much, and particularly about the merits of HRV for behavioral change. If you use the same device and conditions as longitudinal trends for multiple (at least 2-3) weeks that may be the one way to get something useful from the measurements. Data for overnight sleep with minimal motion and using RMSSD is the best proxy for real HRV. The reason to look at trends rather than any given night is that it more likely represents something, even though you won’t know with certainty what the “it” is. Keep in mind there are no data, no peer-reviewed evidence, to show that HRV fluctuation in-person has any correlation with health outcomes. Share Readiness Scores These are proprietary scores that integrate different metrics for each of the wearables: no algorithms have been disclosed. They are unvalidated against health outcomes. In a review of 14 composite health scores of readiness and recovery, HRV contributed 86% to the scores, followed by reading heart rate (79%), physical activity and sleep duration (both at 71%). That review noted the substantial variability in measurement protools and lack of standardization. Sleep staging is notoriously inconsistent and inaccurate by these sensors, which adds further to the HRV uncertainties for what the scores, which use sleep stage data, mean. Only resting heart rate has been shown consistently across devices to be extremely accurate. I’ve made a Table to summarize what we know about which metrics are included, the scores, any peer-reviewed studies that compared the readiness score with health outcomes, and the corresponding (if any, NA-not available) citation. You will note that some companies do not use the term “readiness," such as WHOOP for recovery, and Garmin, which has 2 different scores, one of which is Body Battery. Eight Sleep uses the term “Fitness Score.” They all include HRV; Apple includes a new metric they call “Recovery HRV” which among other components uses 7-days of sleep, but it is unclear what this means or how it is differentiated from other scores (there are clearly no data for outcomes). We have no knowledge of how the different components are weighted or whether any of these scores are better than resting heart rate, HRV alone, physical activity, or any other single metric. Since none of these are standardized, they are not interchangeable, so if you get a 90 for Oura that has no relationship to a 90 on a Google Fitbit Air. Notably, the company can update its algorithm for readiness score at any point without notification to device users. Without any useful evidence of actionability for these scores or established relationship with health outcomes, it is hard to make a case for their value. At the Apple recent announcement they showed their Readiness score (0-10) on the watch (Figure below) but there are no published data on this score, not even on their website. It’s available only on their new Watch Series 12 or Ultra 4 [of course, ;-)]. That exemplifies the problems with these scores, lack of data and evidence for being meaningful to promote health. Perhaps the best study (which isn’t saying much) is the WHOOP Recovery for golfer performance, because it did correlate with an objective outcome, even though there was no control group and the authors were all from the company. Among the 389 pro golfers, an absolute 10-per cent point increase in Recovery score was associated with about 0.5 fewer strokes per round. But that’s hardly a health outcome! WHOOP is also conducting a study in over 2,700 runners to see if their recovery score will be linked to less injuries and improved performance, but that is not yet published and has no control group or randomization. Putting This in Context For two decades I’ve been enthusiastic about the potential for digital health and particularly wearable biosensors. Over the years, we’ve seen some great progress for their ability to promote physical activity and accurately detect atrial fibrillation (the first FDA cleared deep learning AI for consumers). That work was the subject of rigorous research. But there are holes in the data and evidence for other metrics. One notable one is the “VO2 max” story that I wrote about earlier this year. At that time many subscribers asked me to cover heart rate variability, which I finally got to here. When I dived into the research and publication for HRV and readiness scores, I expected to find at least some that were of high quality and demonstrated their utility by linkage to health outcomes. To my surprise, I found none. The wearable sensor measurements for HRV (PRV) are, for the most part, accurate, but that validation work has only been done in small studies of healthy adults and does not take into account the long list of factors, from the device, software side, and the user side, that affect HRV measurements. Moreover, this metric chiefly relies on optical sensing and, as we have learned for heart rate PPG sensing, may be less accurate in people of color. Keep in mind that all of the health outcome association evidence comes from ECG-derived HRV; none are from wearable sensor data. I will repeat the key point: there's no peer-reviewed evidence to show that in-person HRV fluctuation—or efforts to raise your HRV— has any correlation with health outcomes. For those of you who look at your HRV on awakening, or even 2+ week trends of it being low, I hope this context helps to relieve any anxiety. Yes, low HRV (not PRV) has been shown to increase risk of some diseases as summarized above. But efforts to raise your HRV—a surrogate metric— has not been established for improving any health outcomes. HRV does not have any evidence of causality (the genetic evidence actually goes against this possibility). In this summary, I have not included data for other wearable sensors such as Polar, Samsung, Withings, Suunto, Amazfit, Coros, Ultrahuman, or additional mattress sensors. These are beyond my first-hand experience, and as far as I know from my in-depth review none have any peer-reviewed published data that differ from the 6 sensors I’ve reviewed here. From the points I’ve gone over above, we’re not ready for readiness scores. Besides being proprietary, they are predominantly based on metrics that have their own issues. It’s compounding the problem, like building a house without a solid foundation that has never undergone a rigorous inspection, and then selling it. Like I mentioned for PRV, you can look at trends over weeks rather than any single day, to get a handle, but even that may not be helpful. There’s simply no evidence that these scores meaningfully relate to health outcomes. I’d emphasize they might, but that requires doing prospective or randomized studies to prove it. None exist. There’s great promise for HRV/PRV utility_. For example**,**_ Prof Maiken Nedergaard, who discovered the brain glymphatics that are essential in eliminating metabolic waste products from the brain during sleep, has posited that HRV could be a non-invasive marker for neuromodulator oscillations, brain-body regulatory circuits, and brain clearance. That would be extremely useful, but like everything else on HRV and readiness scores it requires solid research and validation. The lay media isn’t helping much to get the story straight. Earlier this year The Economist published a piece entitled “The most useful indicator of your overall health” which ordained HRV as an “accumulated stress score.” That’s akin to the false assertion about VO2max: “V02 max is the singular most powerful marker for longevity.” As I’ve summarized here, that is not established. The fact is that so many things can lower HRV, including physical exercise (especially an intense workout), reduced sleep quality, stress, the list above, no less the device, signal, and software. Whatever fluctuations observed have not been correlated with any health outcome. Sadly, “datamaxxers” are widely using HRV and readiness scores that have never been validated to mean anything. We already know that for some people using the sensors for sleep metrics, it can induce “orthosomnia,” an obsession to get high sleep quality, with associated high levels of anxiety. In an experiment done by a company to promote sleep quality for its employees, “For those employees who did use the trackers, many reported feeling perfectly rested until their tracker told them they had had a terrible night. Others were told that they had slept like a baby when they had actually been lying awake worrying about the quality of their sleep. “ The same problem can result from preoccupation with HRV or readiness scores, with anxiety that would lead to further reduction in both. It you are using a wearable like >100 million American adults, it’s OK to look at these data, but contextualized with the major caveats reviewed here. If you are one to require evidence that HRV or readiness scores are linked to health outcomes, you may not even want to look. The companies make it hard to turn them off! Let me end with the companies that make and sell wearables. Apple’s doubling down on HRV (24-fold more reporting and heart rate very 5 seconds) and introduction of a Readiness score tells us that consumers have bought into these metrics and they are joining the club. However, all of this is occurring with a backdrop of tens millions of users, claims about the data that are not backed up by adequate evidence, marketing way out in front of whatever limited data exists, and not being transparent about their readiness score algorithms. The companies can well afford to do the research that is needed to connect these metrics with health outcomes show, once and for all, that increasing HRV or using readiness scores promotes our health. If they believed and invested in the products they are selling, we’d not be in this position of not knowing. That’s essentially where we are with HRV and readiness scores. Perhaps someday this will change and we’ll have good reason to embrace them. NB: I wrote this post. No AI. I have no conflicts of interest with any of its content. Loading... Ground Truths has 215,000 subscribers from every US state and 214 countries. There are over 300,000 followers of Ground Truths so more than 90,000 folks who can easily convert to be free subscribers. Your subscription to these free essays and podcasts makes my work in putting them together worthwhile. If you’re not a subscriber, please join! If you found this interesting PLEASE share it! Share Ground Truths The proceeds from all voluntary paid subscriptions go to support our summer internship program. It enabled us to accept and support a record number of 62 summer interns that joined us in 2026! These are high school, college and medical students selected from thousands of applicants. We couldn’t do this expanded program without the funds coming in through Ground Truths. Thank you!
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