Thank you so much for writing all this out. I may not need this information right now (no money for gear) but this is still so intesting. I'll come back to this when I've got the money to spare.
The voltage, state and current draw and other cool stuff can usually be found from /sys/class/power_supply/BAT0/ you just have to make a small script to calculate what you need from that. This requres some knowledge, but it's one way to do it.
Thank you so much for writing all this out. I may not need this information right now (no money for gear) but this is still so intesting. I'll come back to this when I've got the money to spare.