[TouchPad Q&A, Help & Troubleshooting] jackygogo:
I noticed the links in this post doesn't really lead you to the debrick guide, so I am writing this.

P.S. I am ONLY reporting my experience as is to my HP Touchpad 16GB running CM-tenderloin. I am not in any way responsible for developing this method nor am I responsible for any extra damage that might happen to your already problematic Touchpad. Good luck, and research is your best friend.

I got this question mark battery problem as well and after doing some research I thought my HP Touchpad was gone for good. Then I saw this post and after reading it it inspired me to try the tpdebrick made my jcsullins. And... it worked and my touchpad is back to normal (with everything data intact as well, to my surprise!). My problem was similar to described by other posts in this forum: the touchpad was discharged until it turned off, and then it was left that way for a long time, and when I tried to charge again, it would first give me a flashing home button and then the battery with a question mark after a long time of charging. No matter how long I charged the problem persist, and the device refuses to go into recovery mode no matter what I do. WebOS is unable to detect the device as well, but the PC was able to recognize it as Palm or UQSB something something something (I forgot what it was). After this problem I did not do any battery change or hardware changes. Just me, the question mark battery, and the tpdebrick buigde by jcsullins.

So if you have this problem and absolutely cannot get into the recovery mode, give tpdebrick a try. I used tpdebrick-v004 by jcsullins: rootzwiki.com/topic/38786-tpdebrick-v004

Follow through the steps in that post and it should be okay. But, in case anyone needs it, this is all the steps I did:

0) While my screen was displaying the question mark battery, I pressed Power + Home + Vol Up + Vol Down for 30 seconds while USB plugged into PC to make sure everything turns off (i.e. black screen, no flashing home button). This step may or may not be necessary since part of the debrick process you need to do Power + Home + Vol Down, and it will most likely do the same thing. But just in case.

1) downloaded Ubuntu 12.04 32bit, downloaded webOS 3.0.5 doctor (this was in zip format, and I had to change it to .jar extension), and downloaded tpdebrick-v004.zip from the link above. You can download webOS doctor and tpdebrick in Ubuntu so that you can follow the instruction as written without any trouble, but I did it in my Windows and I fetched it from the Windows storage in Ubuntu. Whichever is easier for you.

2) Downloaded Universal USB Installer and made a bootable USB of Ubuntu. Followed instruction here: ubuntu.com/download/help/create-a-usb-stick-on-windows

3. Boot from USB and run Ubuntu OS

4. Found and moved the tpdebrick.zip and webos jar into the Ubuntu OS Downloads folder

5. Followed steps 14 to 23 from the debrick instruction by JC above. (Basically run terminal, unzip tpdebrick-v004.zip, and hold power + home + vol down for 30 seconds, and run script, and then run "sudo ./tpdebrick XX" where XX = size of your touchpad)

6. Wait patiently for 5 - 10 minutes, and then it says All Done. By this point, my HP touchpad rebooted back to the original state. If this does not happen for you, then you might need to keep researching! Good luck!

NOTE: After the process, my touchpad rebooted back into CM, and I noticed the battery was fully charged. So, obviously there was no problem with the battery nor the charging process. My problem must be due to miscommunication with the battery status.