When the HP Touchpad went on sale for $99, I bought one and offered to buy my daughter one as well. She declined but asked for mine later as a birthday present. I bought another one for myself. Due to the limited number of WebOS apps, I rooted mine to Cyanogen Mod 9 Android. No one told me that it is possible for Android to drain the Touchpad's battery to the point it will never recharge. I bricked it! Fortunately, a new battery was an option.
Using ifixit's excellent guide on replacing a Touchpad battery, I opened the case and proceeded to an almost total disassembly of the unit. HP designed the Touchpad in such a way as to require this, going so far as to place the battery to motherboard connector on the bottom side of the assembly. This requires one to remove the motherboard and battery as an assembly - after disconnecting every other device in the unit!
The dissasemby went smoothly as soon as I removed the digitizer and display. As forewarned by the guide, I broke a couple of the retainer clips. After this, it was just a matter of following the crystal clear, step by step instructions. Reassembly was also straight forward, although I had to reverse a couple of time due to the fact that I had not made sure a couple of cables were in front of and not behind the motherboard/battery assembly.
The Touchpad works great once again. The digitizer and display are not as tightly connected to the case as I would like due to the broken clips, but with the case on, it is not noticable.
This repair took about three hours. Next time, if there is one, will take less than two.
Don't let your Touchpad discharge to the point of no return. But if you do, buy a battery and follow ifixit's great guide to resurrect it!
Make sure all the cables are clear before you put the mother board and battery back in the case.