Battery not holding charge

[GSiFan]

Tricky because access is difficult in much of the car. I'd probably try the fuse boxes first. It'd be relatively easy to remove one side of a fuse and stick a multimeter on it to check for any quiescent current draw. I guess a voltage across the fuse would also suggest that there was some current through it. The trouble would be that some circuits, if you interrupt them, might operate in a different mode afterwards. Not really sure on how to test circuits in this way. Someone will be along... Paul

[Journeyman]

Just switch multimeter into amps and put it in series with batt this will confirm if theirs any parasitic drain

Follow advice from Critch. Max parasitic drain should be 50mvolts.

[GSiFan]

... But not the source of the current drain. Paul

[Froggy]

Could it be caused when the cam chain guide broke and the engine stalled after the inlet valves met pistons?

[GSiFan]

I don't see how that could have caused an electrical fault resulting in a current drain. Paul

[barks]

If the battery shows a normal voltage whilst left off the car it could still be damaged as its the battery's capacity to deliver the required current that is important. Once it's connected to the car if the battery is faulty and is asked to deliver a current that it has trouble doing it can kill it and the voltage will also drop.
The battery may or may not be faulty but I'm saying that just because its ok off the car dosent mean its ok.
As already said you can carry out a battery load test with multimeter, this is carried out by placing the multimeter in line from the battery terminal and the load on the battery will show on the multimeter. You can then switch things on and off to try and find a culprit if there is one. It maybe ok until you lock the car for instance. Or closing the boot may not show a drop in which case the boot light is staying on.
Regards