Last Monday I helped out my neighbours by diagnosing their CR-V with a drokked battery (not just gone flat, but drokked). I also diagnosed their Beemer 3 series 'no start/key stuck' (it's an auto and was in reverse

Friday I installed the new battery they ordered on the CR-V and topped up the oil and coolant (usual modern car neglect).
Saturday morning I went to use the C5... Flat battery

Saturday afternoon I use the BB4, go to the barn, head home to wash it before Mimms Sunday and stop off in Maccy D's on the way. Sit in the car park with stereo on for literally only 5 mins... Radio goes dead. Uh oh... Try and start it... Flat

So the moral of that story obviously is... If your neighbours car battery goes flat, don't offer to help them!