Support multiple batteries

[mark7]

Previously, only data on the first battery found was collected. Some
laptops (like the Thinkpad T470) have multiple batteries, resulting in
the charge from only one being logged.

Treat all batteries as one large "aggregate" battery and store data on
its charge.

[petterreinholdtsen]

I would imagine it make more sense to record information about each battery individually. Why do you believe it make sense to store the combined values?

[mark7]

Well:

• Existing software that I use, like i3status, aggregates the charge.

• Multiple separate batteries would require UI and logging changes (e.g. all the commands would need to be parameterized on individual battery), whereas an aggregate battery permits continuing to use the software as-is. I can't say that there's no chance that someone would have a use for treating them separately (e.g. if someone physically swaps batteries, which is one thing that someone can do with a laptop with multiple batteries), but I simply am interested in how much life the laptop as a whole has remaining -- the location of the individual charge isn't very interesting, but how much longer the laptop as a whole has to run is.