Limiting charging to 80% to improve battery lifetime

[pavelmachek]

Affected hardware version

Bangle 2

Your firmware version

Any

The bug

Bangle seems to charge to 100%. That will reduce battery lifespan from maybe 8 years to maybe 4.

Given that battery can last for few weeks, limiting charge to 80% might be good idea (at least for times when you don't plan to use GPS).

So far I have this: it attempts to vibrate when we are at 80% to make me disconnect the charger. If there's hw trick to stop the charging, that would be better. It probably needs more experiments / calibration to vibrate at right time.

https://gitlab.com/tui/tui/-/commit/b3780e1d169fdd09fc1eb0db94b2143dfb1b68d8

Installed apps

No response

[bobrippling]

Sounds like a cool idea - I do find that if, while charging, the watch reports 100%, it's actually more like 80% when I unplug, since the voltage read is that of the battery + what the charger is putting in, so I figure if the watch is at 100% for a little while, it's ok since it's more like being at 80% anyway.

But halting changing via hardware sounds good - I do the same with my phone. @gfwilliams do you think this is possible with what the firmware can do?

[pavelmachek]

So for me, if I unplug around 95% indicated while charging, I get to ~80%, but it is not too consistent. (Which is what the code does).

I'm experimenting with turning on backlight & gps at ~90% to slow charging down (and maybe getting more consistent results from the voltmeter). But if there's GPIO to control charging, that would be even nicer :-).

[gfwilliams]

I'm not aware of anything you can do in hardware to stop charging - that's not to say it's not there, but I never found it. You could try fiddling around with some of the unused pins while charging in case one of them does affect it.

One thing to consider is I know a full charge will reduce life in a phone, but I believe that can be to 4.3v or so. Bangle.js only charges to 4.2v absolute max, so you may find that it's already charging to what a phone would consider 80%

[gfwilliams]

... You could of course have some external hardware if you want to do it. Like you could power the charge cable from a Jolt.js, then advertise on Bluetooth when there's enough charge and get the jolt to turn it off

[pavelmachek]

Yeah, so the "external hardware" that cuts the charge will be "me" in this case :-).

And yes, 4.35V charging is done in some new phones, but I believe those have special cell chemistry. I don't believe Bangle.js2 has one of those cells.