In LabQuest versions 1.5 and earlier, a bad battery can cause the following behavior:
When operating on batteries, the Home menu will open, but tapping any selection appears to do nothing, or the action is delayed by many seconds.
When connected to AC power, the same unresponsive behavior can be seen.
In addition, the battery icon gives different responses each time it is tapped. For example, repeated tapping may give charging, charged, low, etc.
The problem is caused by a bad battery giving the CPU frequent status updates.
Solution: Replace the battery.
In versions 1.5 and newer, a bad battery will not cause the system to be unresponsive. However upgrading to 1.5 or newer will not fix the battery itself, and the battery will still need to be replaced.