Yeah the battery warning light's fine and we tested the alternator with a bit of kit that works similar to a voltage reader but it has LED's on it instead, and even on high revs the alterator only puts out 12.5volts.

My mate reckons that the battery is probably just recovering while it's standing hence why the alarm works ok after a while.

I'm stumped then. I'll try the earth points like u said at 1st and see if that makes a difference