An update, I used the charger to directly charge the battery as described here: viewtopic.php?f=1&t=13212
twice, first for 15 minutes then for 30. After the first time I plugged the battery into the robot, and turned it on. The power button lit up green for a second, but then went to red and then turned off. I figured this was a sign of success, so I charged it again for twice as long, but when put into the robot it stayed on for only a second, just like the first time. I kept the battery in the robot and plugged in the charger. The power button pulsed orange, just like normal, but only for about ten seconds, after that the power button started blinking red again.
Still lost at where the problem could be.