Re:Some Google Pixel devices shutting down at 30% battery
by andrewstuart2 on Wednesday December 28, 2016 @01:34PM
(#13272514)
My Nexus 6 did this quite often, as does my wife's HTC One M8. It definitely could be an Android issue, but I think it would have to be a particularly egregious and obvious mistake.
If it is software, I'd strongly suspect something at kernel level, since quite a few times in my experience, the shutdown is too quick for a safe shutdown. Userspace seems to get a notification that battery is low because it usually gives the "shutting down" alert, but then just shuts off in a suspiciously short amount of time.
I'd be more likely to think it's probably something in the battery/power stack that's not managing or reporting the power well. Discharge/voltage curves are not at all linear, [1] [2], so it's logical that issues with immediately available voltage might start to affect the device around the 30% level. Additionally, as another commenter has mentioned, the discharge curve is dependent upon temperature [3], so a sudden drop in ambient temperature will eventually have a direct effect on the reported voltage.
I'm not exactly sure what kind of metrics are commonly used for reporting battery percentage, but I am about to read a few (okay, maybe half of one) Arxiv papers that came up in a search. [4] Presumably, it's strongly based on some voltage modeling and I can imagine that would have a hard time coping with external factors beyond its measurement capacity, like ambient temperature drops. I don't suppose a user would be happy to see their reported battery percentage drop like a rock immediately upon stepping outside.
I really don't know where I was going with all that, except I guess to say that my gut says Battery "percentage" is a bit more an art than a science. That is to say, there are psychological reasons not to report based on voltage directly (it may go up if you step into a warmer room; "Wat?"), and I can imagine any metric is going to have its strengths and weaknesses, because you really can't account as much for user behavior that changes important physical conditions of the battery.
If it is software, I'd strongly suspect something at kernel level, since quite a few times in my experience, the shutdown is too quick for a safe shutdown. Userspace seems to get a notification that battery is low because it usually gives the "shutting down" alert, but then just shuts off in a suspiciously short amount of time.
I'd be more likely to think it's probably something in the battery/power stack that's not managing or reporting the power well. Discharge/voltage curves are not at all linear, [1] [2], so it's logical that issues with immediately available voltage might start to affect the device around the 30% level. Additionally, as another commenter has mentioned, the discharge curve is dependent upon temperature [3], so a sudden drop in ambient temperature will eventually have a direct effect on the reported voltage.
I'm not exactly sure what kind of metrics are commonly used for reporting battery percentage, but I am about to read a few (okay, maybe half of one) Arxiv papers that came up in a search. [4] Presumably, it's strongly based on some voltage modeling and I can imagine that would have a hard time coping with external factors beyond its measurement capacity, like ambient temperature drops. I don't suppose a user would be happy to see their reported battery percentage drop like a rock immediately upon stepping outside.
I really don't know where I was going with all that, except I guess to say that my gut says Battery "percentage" is a bit more an art than a science. That is to say, there are psychological reasons not to report based on voltage directly (it may go up if you step into a warmer room; "Wat?"), and I can imagine any metric is going to have its strengths and weaknesses, because you really can't account as much for user behavior that changes important physical conditions of the battery.
[1] http://www.powerstream.com/AA-tests.htm
[2] http://www.ibt-power.com/Battery_packs/Li_Ion/Lithium_ion_te...
[3] http://www.ibt-power.com/Battery_packs/Li_Ion/Li_Ion_DiscTGp...
[4] https://www.google.com/search?q=battery%20percent%20site%3Aa...