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

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. [1] http://www.powerstream.com/AA-tests.htm http://www.powerstream.com/AA-tests.htm [2] http://www.ibt-power.com/Battery_packs/Li_Ion/Lithium_ion_tech.html http://www.ibt-power.com/Battery_packs/Li_Ion/Lithium_ion_te... [3] http://www.ibt-power.com/Battery_packs/Li_Ion/Li_Ion_DiscTGph.JPG http://www.ibt-power.com/Battery_packs/Li_Ion/Li_Ion_DiscTGp... [4] https://www.google.com/search?q=battery%20percent%20site%3Aarxiv.org https://www.google.com/search?q=battery%20percent%20site%3Aa...