Ability to limit battery charge to X%

[matejdro]

Is there an existing issue for this?

• I have searched the existing issues

Proposed feature request

Lithium batteries degrade much faster, the closer they are to the 100% or 0%. With these watches, this is made even worse, because, after being fully charged, the watch will potentially spend days being close to the 100%.

To make this problem better, there could be an option to limit the charge to a smaller level (usually 80%, but a configurable level would be even better). When the watch would reach that level, it would stop charging and just hold it.

Alternatively, if the charging circuit does not allow holding the level, it could just turn charging off and on again, so it would oscillate between 79% - 81%.

Alternatives

No response

Anything else?

No response

[matejdro]

Hm, could this be emulated with a smart plug and a watchapp? Need to look into it.

[ericmigi]

seems reasonable, but in the grand scheme of things - lipolys get hundreds of charge cycles before they degrade noticeably. at 2-4 week charge cycles, capacity might go down 1% per year max!

[matejdro]

But that is only for cycles. They also get extra degradation when stored near 100% or near 0% for prolonged amounts of time, right? And these watches are technically stored at near 100% for days after charging.

If 1% per year were true, then all of the original Pebble batteries would not be that shot.

[ericmigi]

older watches had to be charged every 5-7 days 😉 . and still remarkably my OG pebble (one of the first off the production line in 2012), still gets 5+ days!

[matejdro]

Well, my old P2 gets around 2 days max, presumably because its battery was dead (near 0%) most of that time. Presumably you kept your watch in a good condition (not always drained) for most of that time? This is exactly what this issue is about :)

[ericmigi]

Still not sure I understand...if you aren't planning to use your watch for a while, charge it then shut it down.

Ah, maybe the part about zero percent threw me off. I guess what you're asking is to have an automatic stop at 80% so you could charge at 80% and then shut down the watch for long periods of time

[matejdro]

that would also be a good use case, but I'm primarily asking for in-use scenario.

[ItsHarper]

Right, it's about not having it sitting above 80 for several days while it slowly drains to below that level in normal use

[ericmigi]

ah I got it, yeah that makes sense! We're busy with other stuff, but if someone else wants to add this as an optional setting, feel free to go ahead.

[andreyvolokitin]

Can this also be useful for charging 3.7V replacement batteries without adjusting firmware charging curves? If we charge it to 80% we're fully sidestepping the 3.8V overcharging issue

[adipascu]

I put up an implementation of this in #1841, with the phone-side setting in coredevices/mobileapp#318. The limit is configurable from 50% to 95% and off by default. I have only been able to test on a Pebble Time 2, so reports from other models would be very welcome.