What's the trick to get the battery to charge?

[diodelass]

I kinda had the same problem.
I had to open up the device as the contacts were loose. Reconnecting them properly fixed the problem for me.

This can't be the problem for me, because the battery is definitely connecting; using the relevant sysfs handles (in /sys/class/power_supply), we can obtain its voltage, current, and capacity and such - it's just that it never starts charging, and only seems to discharge when present, even if external power is connected. I've double-checked the battery voltage with my multimeter, too, and it matches what the software reports, so I don't think this is a reporting error, either.

It feels like there must be some kind of electronically-controlled switch in there to engage charging mode that I haven't found yet.