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According to my battery graph the phone went from 85% to 0 in an instant. I wanted to add a screenshot, but I do not have enough reputation. The last time I checked it was nearly full, and 7 hours later in the morning it was empty. At home I charged it until it showed 29 percent, but by the time I got to the office, it was 32.

How can this be? How can I prevent it in the future?

LG P990, Android 4.0

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You can provide the link to the screenshot. A user with higher rep then can integrate it with your question, if (s)he finds it useful. –  Izzy Feb 19 '13 at 17:21

3 Answers 3

up vote 1 down vote accepted

It could be a misbehaving app keeping the device awake; I have that about once a month with my Motorola Milestone 2. Did not figure out how to prevent it, but a reboot always solved it.

A proposal how to "catch" it, however: There's an app called DrainGuard available on the playstore. It watches your battery consumption, and gives an alert as soon as it detects a "sudden drop". This helps to notice the "power drain" before the "5% alert" makes a noise and switches your phone off -- so you can either start investigating while the process is ongoing (some time left before "full drain"), or simply trigger an immediate reboot to "kick the bad guy out" when in a hurry.

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A bad battery could cause this.

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Care to expand on that? –  Al E. Feb 19 '13 at 19:03
    
sure, I have personal experience seeing a battery show up as good (50%+ left) and then minutes later be drained. I am not an expert on technically what causes this (bad cells maybe?), but I do know when this happened to me, the solution was a new battery. –  William Feb 19 '13 at 22:30

The actual capacity of a battery decreases as the battery ages through an irreversible fading process. This capacity loss occurs both with active use, correlated with charging cycles, and with inactivity through self-discharge. The device may even come with substandard batteries. However, the amount of loss is linear with time and accelerates with increasing temperature. Smartphones do not typically employ sophisticated techniques for estimating the usable capacity with the basic solution basing on simple charge cycle estimation and then using an offline calibrated lookup table to find the state of charge or battery level given the charge cycle.

SOC estimation in modern smartphones cannot capture the usable capacity of the battery, and thus have unreliable SOC estimation. This inaccuracy manifests as sudden jumps in the battery level, and can result in unexpected shutdown of the device.

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