Flat as a pancake after 12 days

[the dodger]

I've left my car for two weeks before without connecting the trickle charge - several times. If it's going to be more then I plug it in and over the winter usually fire it up a few times as well. I last used it on Bank Hol Monday but yesterday when I turned the key NOTHING! - not even any warning lights on first position! Car in (narrow) garage battery-side hard against the wall so I thought I'd plug in the Draper 300mA charger - and wait. Lots of clicking going on around the door-locks then ZAP! the central locking energised and locked me out! Early Chim with key locks so I thought no problem. Was it ! - Key operation failed, still couldn't get in.

Fortunately as car in secure garage the roof was off so I could reach in and twist the door opener but I wondered - Is there another way in for this situation?

Left charger on overnight and today the key operation worked! (just) and door now unlocked. Strange that when the battery voltage dropped the alarm didn't go off???

Anyway, any ideas why the battery flattened itself? New siren fitted a few weeks ago but other than that, no changes.