I've noticed that Ubuntu 12.04 restarts instead of hibernating or when the battery power is below the critical level, and then continues restarting until the battery runs out, and power is lost. Is this the normal default setting, or is this atypical? I can't see why it would have been designed this way intentionally - it seems counter-intuitive (aside from the obvious risk of data loss). When I first installed Ubuntu 12.04, it would suspend when the power was critically low, but this is no longer the case - why did this happen?
Suspend is normal when power is low. Open up "System Preferences" and click "Power". There it will tell you what it does when the power is low or system idle etc.
If you want alternate power management then you can always install Jupiter.
After you've done that logout and log back in. If you don't like it then you can remove it with: