Cursor moves erraticly, by itself

No doubt this problem has been posted before now, but I can't find a suitable answer.

A few weeks ago my cursor started behaving strangley. It moved erraticly, without me touching anything, changing screens, opening new windows and more. I tried a variety of fixes, disconnecting the wireless (Logitech) mouse, putting the MBP on a table instead of my lap, and these seemed to cure the problem temporarily. However the problem has become more frequent and today I had a long period where the MBP was unusable. I disconnected all peripherals, power, took the back off and blew out the dust but everytime I re-booted the problem was still there.

I turned the MBP off for 10 minutes and re-started it on a sheet of card and it's running OK now. If I remove the card and the MBP is on the desktop the cursor starts to move again.

Two more points; the MBP seems to be running cooler on the card, the battery is slightly bulged on the outer corner.

I'd be grateful for any ideas on the cause of the problem, and a remedy.