What is the Battery Capacity in mAh for Sense?

[eezeepee]

Just curious about it but does anyone know what the battery capacity in mAh is for the Sense? It's not listed in the specs and no review or listing has it mentioned as well.

I have a charging meter which I haven't used to go from 0-100% yet but yesterday I did an estimate and got a total of only 165 mAh from a charge of 32% which got me 53 mAh. That would be be way smaller than the usual 300+ mAh by the competition. 

I will try a 0-100% next time. It's going to take a several days since I'm at 76% this morning. 🙂

Moderator Edit: Clarified subject

[t.parker · Accepted solution]

Just run GPS and it will take best a few hours to drain it to 0% 😉 

According to iFixIt teardown 

"The battery is a 1.02 Wh (266 mAh @ 3.85 V) cell, slightly less potent than the 1.17 Wh pack from the Apple Watch Series 6 and a far cry from the 2.16 Wh cell in the Xiaomi Watch."

[eezeepee]

Thanks! Totally forgot about iFixIt. Weird how I didn't find that myself searching "Fitbit Sense mAh". I see it now when searching. Was probably just scrolling too fast. 😆 Still a pretty small battery considering how it can get multiple days easily.

I think that means that either my meter is off or the battery percentage was a little too generous in saying 32%. I'll still do my own tests to see which one it is. It could be both. 

[t.parker]

@eezeepee the battery life is prolonged by reducing framerate to 24fps (Apple and Samsung watches do 60fps) and using very simple low-powered GPU (again, Apple and Samsung watch support Metal/GLES3+, can render 3D graphics with 60fps but there is a price to it - battery life). Fitbit cuts some hardware and software corners to achieve better battery life.

The battery is mostly consumed by sensors and screen activity. Also, the SDK for developers allows doing a lot more if you develop for Apple or Samsung which makes it more likely to reduce battery life by using third-party apps (of which gallery is much richer, too). Apple HR sensor (I didn't check Galaxy Watch sensor frequency) sampling frequency is equal to PolarOH1 (which probably is the reason why AW is considered among the best HR wrist monitors but pays a price of battery life).

It's more like a trade-off. Deliver high-end products but shorten battery life or go low-end but give days of battery. For me, the "sweet spot" is what Garmin does - using a transflective display and no touchscreen (I dislike touchscreen on wearables because of the behavior in wet conditions) that can be always-on at the minimum battery cost so my Fenix lives 5-8 days (sometimes more, depends on GPS and external sensors usage). If it was AMOLED, the battery life would drop a lot. However, not everyone likes washed-out colors of transflective display (that was a huge shock when I moved from Fitbit Ionic to Suunto Spartan years ago 🙂 ). Some people prefer the smoothness of AW and they can accept charging every night, others will prefer nice crispy display but will accept simplicity if they are given longer battery life, and others will prefer lower quality display if the watch delivers other functions. The market is big and there's something for everyone.

[eezeepee]

Yeah I can definitely tell the frame rate is lower on the Sense from coming from a Fossil Gen 5. Definitely not as smooth. The Sense is noticeably brighter though even at dim.

Interestingly, the newer Garmin watches are touchscreen and AMOLED and still claim up to 11 days of battery. I would be interested in something like the Venu 2 but would like it's sleep tracking to be up to par with Fitbit especially considering the price. Interestingly, their Hybrid Vivomove, at only $179 USD, does a better job at it than any of the other more expensive models. Still not as good as any Fitbits. So one would think the algorithms could be updated to be improved.

[t.parker]

Mind that some models (like newer Fenixes) are equipped with batteries 400+mAh so it affects battery life surely. New Garmins with AMOLED and touchscreen are totally not for me (including Epix 2). This is that sacrifice I mentioned. Venu series doesn't support in-watch navigation and a few other crucial for me features. Epix 2 is somewhere in the middle but doesn't meet my requirements either (and let's face it - it's ugly). Luckily, the new Fenix 7 comes with a transflective display and a touchscreen that can be turned off (yet, I'm not gonna buy it as it's not enough of an upgrade compared to F6Pro to justify the purchase). The battery life of Garmin is controlled with plenty of power-saving options (several GPS modes, full control over all the sensors, Fitbit has just started adding those in Sense and Versa 3 models) but if you compare the battery life of AMOLED vs transflective displays, there is quite a difference. I believe, when battery life is compared, the AMOLED isn't always on, which would drain the battery in no time. Also, in case of an emergency, you can charge the watch while still tracking the activity. Became useful quite a few times. I tend to forget to recharge my devices and a few times before riding or running I found out the battery was almost dead. Who knows, maybe AW users prefer short battery life because charging becomes a habit :D.

Sleep tracking is one of the features I'm least interested in (sometimes I look at body battery graph but to be honest, I know better how I slept than any watch can tell me 🙂 so it's more like a "nice-to-have" feature than "must-have"). I'm mostly after the sports tracking features and hardware and software integration. It tells me a lot more when the watch tests my FTP during cycling or measures HRV during activity to provide real-time performance metrics rather than it gives me a sleep score which usually is too broad to tell me anything useful 🙂 But I guess it just comes with needs. As I said, the market has something for everyone.

[eezeepee]

Yeah, there are Wear OS devices with that two display tech as well that saves a lot of power for sure. You get to have an always-on display yet more battery than just having a twist to wake. I don't find charging once a day too huge of an issue because when you have fast charging, topping off while showering and getting ready gets me plenty. That's how I do it with the Sense but it is nicer doing it every 2-3 days rather than daily. The problem with my Fossil was I definitely couldn't get a whole day's worth if I did sleep tracking and/or an hour of exercise tracking. So I was definitely needing two charges and that's annoying for sure especially with a proprietary charging system, but most of these devices do. Everyone needs to get on Qi charging already.

[t.parker]

Twice a day? 😮 I never had a chance to use Fossil (although I have heard a lot from a Google engineer who worked on it until the project got canceled) but I've seen such a bad battery consumption only on the first Galaxy Active watch. My wife was using it for a while but got tired of charging it so frequently and gave up on it. The always-on display is a must-have for me due to using a watch as a bike computer (attached to handlebar). There are certain activities that won't make it easy to use gestures to wake up the watch.

By the way, you mentioned "(...)still claim up to 11 days of battery". Such statements must be always taken with a pinch of salt 🙂 I'm not saying it's not true. It's only the good part of the truth that suits marketing needs 🙂 In terms of battery life, I think it's more important the watch will keep the charge long enough when it's really needed and must not fail. If I know that I go for a few hours bike ride, I need to be sure that GPS + any other features will not drain the battery too early. So every manufacturer tries to show the best side of power consumption. There are crazy high numbers (often expressed as hours, because it looks better than days) for "doing almost nothing" type of usage (like this "11 days"), then the GPS, then maybe when playing music which seems to reduce battery life just a bit, etc. But often it has nothing to do with real-world usage. For example, Garmin won't tell me how long I can use my watch with GPS+GALILEO (with sampling 1s) when connected to external devices (HR, power, etc.) and in the evening when I need to turn the backlight on. Then all the marketing numbers just drop and crash when they meet real-world use cases (rather than perfectly prepared lab tests) 🙂 

[eezeepee]

Oh I know that about the battery claims. It's usually under ideal conditions and is more like the maximum. I wouldn't be like the people wondering why the Sense gets 2-3 days but is advertised for 6. 

[Guy_]

@eezeepee , @t.parker , interesting topic thank you.

@eezeepee  - it will be difficult to measure your charge because lithium batteries use a constant current charging which varies on the state of charge. It starts out at about 300ma and ends up at 1ma and 0ma when fully charged.

You would have to note for every % change over about 75 minutes to get the total charge applied and of course due to losses it should be more than the capacity of the battery.

Also regular daily charges may reduce battery capacity quicker as each charge ages the battery to some extent.

Doing infrequent charges means you get more continuous measurements of your vitals.

@t.parker  - on the fly charging is possible with a Sense, with a battery backup unit attached to the charge cable you can wear the watch and charge at the same time, but during charging a lot of features are turned off, obviously heart rate can't be measured as it's sensor is blocked by the charge cable.

[t.parker]

@Guy_ I know, and that's the beauty of being able to use external sensors so all the features could still work while charging and tracking the activity. Otherwise, it's always going to be either charging or tracking.

To make the battery last slightly longer (for all AMOLED devices) it's worth not going crazy on clock faces which are very colorful and bright. The more AMOLED black the better chance the display will stay around its power consumption baseline. The dark grey colors consume slightly more power (this is the reason why Always-On looks the way it looks on Sense). Peeking at the watch several times (and some users do it addictively checking steps or HR) within an hour and leaving the screen on for a couple of seconds each time may contribute to the overall power consumption. Another reason why I find transflective display more useful for me (wasn't Surge released with transflective display?).

[eezeepee]

@t.parker The Surge was a Monochrome display.

[t.parker]

@eezeepee looks like it was Blaze, my mistake.