It is said that the battery should be first charged before doing an update.

But what is the reason for that?

Is it:
1. To prevent the device from an unfinished firmware update in case of a to low battery

ir is it also
2. The OS saves the value for 100 % battery capacity somewhere and so, can't be fully loaded to 100 % again, when the update
was done at 90 % battery capacity, setting the 90 % battery capacity to maximum capacity. In other words 90 % gets the new 100 % value.


Is 2 possible or is battery management done without the support of the OS?

I don't know the answer to this exact question, but I do know the battery management is done in software, and that if you brick the device, with a dead battery, you can not charge the battery, nor reflash the device, without an extra battery.

The case here is 1, and the battery info (full charge etc) is stored in a chip in the battery AFAIK

That seems to make the most sense as well, or things could get really crazy with multiple batteries.

The average required battery capacity is anything more than 50% for flashing the firmware.

Number 1, that's why it is recommended to calibrate the battery at least one time per month.

If the battery meter is like on N8x0, then it's not very accurate except with a fresh battery. Basically, if you charge it to full you'll know it's full.

Thank's a lot for answering my question.