Battery Alarm Even on Mains

Hi, newbie here. I've done a search but cannot find an answer to my question.

I have a Tosh Satellite 1130-Z24. It works fine apart from the battery alarm starting at random times, even when the machine is on mains supply, eventually it just shuts off. I have cleaned out the heatsink and applied new heat conducting grease and it made no difference. The fan seems to operate normally so I do not think it is an overheating problem.

Has anyone else had or heard of this problem? I should add that it does the same even with the battery completely removed.

Thanks.

 

As an update, I stripped the machine down to it's compnent parts today and checked all the connections and that everything was clean. On reassembly the battery steadily recharged until the power meter showed it as full.
The laptop then ran happily for about three hours (on the mains supply) until the battery suddenly seemd to discharge and the alarm started. I shut the laptop down and have removed the battery and restarted it on mains only (which I am sure I've tried before). So now I'm monitoring it to see if the symptoms are repeated without the battery in situ.