One night I allowed my Nexus 5 to upgrade to the latest Android version (Marshmallow) but from next morning my phone was behaving very strangely.
It kept restarting randomly and became almost useless and completely unreliable.
The Problem
The problem seemed to be related to battery calibration information. Upgrading to Marshmallow somehow corrupted or changed this information making the phone unaware of its accurate battery state.
The Solution
Following these steps cured my phone.
- Use your phone until it drains the battery and shuts down.
- Keep starting the phone to make sure you drain all of the remaining battery charge. You don’t need to worry about the amount of charge that the phone tries to preserve. Just do your best as a regular user to drain the battery. Don’t try advanced stuff.
- When the phone is off connect your charger (A/C adapter is recommended over USB) and let the phone charge to full amount without starting the phone.
You can check this by checking the charging indicator that is shown when you briefly press the power button. DO NOT start the phone. - When the battery indicator shows a full battery, start the phone.
- When started check the battery status on the top of the screen. If it is NOT very close to 100% (97% ~ 99% should be fine) then turn off the phone and connect to the charger (step 3).
- Keep repeating steps 3~5 until you are happy the phone is charged to its maximum capacity. This may be less than 100% depending the quality of the battery.
- Then unplug the charger and keep using the phone until it’s fully drained. Do not charge the phone before the battery is fully drained.
Continue above steps several times over a few days and this will solve the problem. It worked like charm for my phone.
I Learnt Today 