I have a periodic problem with my 2010 xc60 t6. Once every 2 to 3 months something kills the battery overnight, such that the vehicle will not start without jump assist in the morning. Even low power stuff like door locks don't work. Had the battery tested a couple of months ago and it was ok. When the battery is charged the car starts great. One thing possibly of note, there is an aftermarket remote starter on the car. I hadn't used til very recently; the key fob needed a new battery. Once a new battery in the key fob, the remote starter worked fine...til today. -15 celcius overbite, -8 during the day. Tried the remote start, went outside to a car not running, a clicking sound coming from under the hood (starter relay I believe). Clicking stopped when remote start was cancelled. Tried using a jump starter (handheld lithium battery) which had successfully started the vehicle after previous incidents. Multiple attempts and no the slightest crank (previous times started on first try -the cold maybe?). Started charging the battery. 4 ways went on. Thought it was alarm related. Inserted mechanical key; nothing. Then the windshield wipers started. Lever was in off position. Tried all positions; nothing. Removed charger, tried to start the car. I think the resulting. Drop in battery voltage caused the wipers to stop. Vehicle did not start, or turn over. No dashboard lights. Because wipers were operating volage from the charger was varying and hence unreliable. Put charger back on for a couple of hour at 6 A. Then tried jump starter again. Vehicle starts, lopes a bit (widely varying idle) and dies. Message board says "reduced engine power". Have seen this on my 2007 S60; on-board computer is confused and can't read sensors properly causing irregular combustion system operation. (Thanks Volvo forums). Will need to disconnect battery for 1/2 hour minimum. Reconnect and drive so the computer relearns the sensors and my driving.

My question, finally, is what could be draining the battery overnight to that extent? Anybody have the problem? Fix it?

Merry Xmas.

Vivo1

PS: on the XC60 the battery was replaced; it was sub par when I got the car. The reduced engine performance problem simply disappeared on its own some time after the new battery was installed. That despite the insistence of my mechanic that the problem was due tu a faulty exhaust gas sensor (narrowly escaped replacing that; $500/part, plus labor, taxes)

V.