We are looking at a freshly installed Ubuntu 11.04 (64bit) on a Lenovo Thinkpad w520 with an Nvidia GPU. The machine freezes eventually during startup on battery. Startup on AC is fine.
The only situation where booting on battery works well is: After a cold shutdown and if the battery has been removed and put back in again prior to booting. Sounds stupid - but that's what I observe.
Sometimes (!) the grub menu is not shown on startup. In this case, the boot process will stop at the stage, when X usually starts. But freeze can also happen after the grub menu has been shown...
1) I find it strange, that it is depended on if plugged-in or not, how the boot process takes place prior to grub. Can anybody explain?
2) Everything might be related to power saving treatment or to graphics driver. But I have no idea.
Should any linux-developer be interested in figuring out what the problem actually is, than I would be very happy to provide detailed info on my hardware / system and also I would be happy to spend time for testing.