Interior Lights Back After Battery Drain!!

This was going to be another battery drain thread, but after jumping the the Rangie all the interior lights started working again!!

Back to the battery drain. Looking for feed back on how quick the becm waking up can drain the battery. I've never got round to changing the RF receiver becoz as we use the RR most days battery drain has not been an issue for many months. Anyway parked up last night at 1900Hrs came out this morning was as flat as a pancake, jumped it no problem, output was 14.4 volts instantly, been sitting a while now and getting 12.5 volts with engine off.

Can an awake becm drain the battery in 12 hours? Or are my interior light issues a sign all is not well with the becm? As always opinions gratefully received.

I would get the battery load tested sounds like a cell is breaking down voltage meter will not detect this cell go high resistance and open circuits the battery