Further adventures! I’ve installed a pair of 706090 batteries (after soldering on leads with the correct polarity). Now I’m going to dig around in the forums to see if I can figure out how to get the charging system to charge the things (they shipped at over 4V when I probed the terminals. I’m down below 30% (per the battery status indicator) but when I check battery status on the tiny OLED, they’re still registering around 3.7 or 3.8V. Is there anything special I have to do to get the charging/voltages kind of ‘aligned’ so that I can trust the battery indicator?
The relationship between cell voltage and remaining capacity is not a linear one.
Did you already go through a full charge/discharge cycle?
Do your batteries not last as long as you expected them to?
I don’t know how far down I should run the batteries - I do know that there will be some watermark that once I fall below it, the internal rp2040 won’t have enough power to run any more (which will then mean I have to take the batteries out and charge them externally). They’re at about 25% right now (per the indicator) but the voltages still read right around 3.7V, which means they’re not charging via the power board (or not charging very much). I’ll report back with clearer numbers/values.