Battery drain overnight?

Hmmm. Tested the battery on Friday 12.6v.

Disconnected for the weekend cos I wasnt using the car - this morning

Possibly a red herring if the battery was colder when you tested it this morning compared to Friday.

Are you doing reasonably long trips? You need to measure the voltage, start the car and measure the voltage at tickover, again at about 1000 revs or so then repeat the last two with your headlights and heated rear screen on. You should see somewhere close to 14.5 volts with the engine running, 12.6 is very low for a charged battery, should be closer to 13.8v.

If you are getting close to 14.5 with the engine running it's likely your battery is faulty, providing you are doing reasonable length trips and not just a couple of miles each way. If you aren't getting that voltage it's likely to be your alternator/voltage regulator.

If I've gotten the voltages wrong can someone please correct them, my memory is terrible since I've been ill.