My car has had issues with getting a good charge from the battery for quite a while. Only ever showed about 12.7v on the SECs and lasted a max of 4 days before battery went flat.

The battery is less than 9 months old and has been tested and is OK. I had the old alarm ripped out and all the wiring, as it played up a lot and I had a new Toad fitted and then the SECs showed 12.9v-13v.

I hadn't driven the car for about 4 weeks, but had it on a trickle charger all that time, but on Sunday, I went to start it and battery was totally flat. The car started with jumper leads though. Put the car away Sunday night with proper battery charger on it, left that on until Tuesday night and went to start it again and nothing! So assumed that the charger was fubar'd. Borrowed a heavy duty charger on Weds night and then started the car yesterday and all was fine with SECs showing 13v. Took the car out to get petrol and take it for a good run, started each time fine.

Came back home and put the heavy duty charger overnight, went to start it this morning and nothing.... dead as a dodo.

Put the charger back on and car turned over ok while the charger was connected but wouldn't fire up. I am seriously pissed off, as I was meant to be taking the car to Cheshire today to have some new parts fitted and this charge issue / alternator[?] investigated.

What can drain a 'fully' charged battery overnight and now also cause it not to start?