|Apparently Thinkpad a30 is not a recent model, so this laptop probably has been used a lot.|
Make sure the main battery is properly seated and making a good connection in it's socket. E.g. unplug it, plug it back in; examine the connection on the laptop.
The laptop is supposed to switch, one way or another, to battery only mode when the AC adapter is disconnected. It sounds like that's not working, probably either because
- something to do with the jack is physically damaged - e.g. a mechanical switching device on it may be broken such that it doesn't switch to battery only mode - you may need to replace the jack.
See response 1 in this:
Correction for that:
The jack in the laptop should move when you wiggle the plug in the jack.
should have been
The jack in the laptop should NOT move when you wiggle the plug in the jack.
- OR - the circuits connected to the jack on the mboard may be damaged, which may not be fixable without replacing the mboard.