Thanks to my previous posts about Amazon Kindle, I have another broken specimen on my desk now. This one seems to have experienced an interesting battery failure.
Kindle's battery has 4 terminals: ground, a positive terminal for power and SDA and SCL pins for I2C communication with the integrated battery management circuit. On a normal battery, the positive terminal is around 3.7 V above ground, depending on the charge level of the Li-ion cell and the I2C lines are on ground level, because they need external pull-ups.
This broken battery however has the positive terminal at 0 V compared to ground terminal while the I2C pins are at -2.5 V. I can't imagine what kind of failure mode could cause pins to go lower than ground, unless the polarity of the cell got reversed somehow. I don't see any way how a failure in the battery management circuit or a loose connection somewhere could cause such readings. I'm pretty sure it's not an artifact of my multimeter either, because the battery can draw some milliamps of current from the ground to one of the I2C pins. For the record, this looks like an original 1830 mAh battery. Date of manufacture is April 2011 and type is 170-1032-01 Rev. A.
The master I2C interface on the Kindle wasn't damaged though, because it boots and reads out battery state just fine when attached to a different battery. There does seem to be a problem with bad a connection somewhere on the motherboard, because it crashes if I lightly knock on the CPU package. Possibly a hairline crack in some solder joint. But that's a topic for some other time.