Overnight Battery Drain.. Can't seem to find any cause
Thread Starter
Newbie
Joined: Aug 2015
Posts: 8
Likes: 0
From: Monterey, CA
W211 E320
Overnight Battery Drain.. Can't seem to find any cause
Hello everyone I'm having a very annoying issue with my 2003 E320. The battery keeps draining overnight! It won't completely die but in the mornings it will go down to 11.3-11.4 Volts. I can't seem to find the issue here. I've tested the car with my buddies Snap-on MODIS scanner. We couldn't find anything other than low voltage codes. We used a multimeter and found that the car has a 1.2 amp drain.. I've unplugged every single fuse and relay including the Audio gateway fuse and unplugged the seat modules without any luck... Anyone ever had this issue? I've already replaced the battery twice! What I did notice however when I replaced the battery the car wouldent drain as quick. In the mornings the battery voltage will be around 12.2 volts but the car would still start.. this of course would last about 1 week until the battery starts draining below 12volts. Anyone dealt with this similar issue? Should I check something else? I was thinking it might be the voltage regulator behind the alternator but I won't be able to test that until Thursday. Other than this the car runs great without any other issues. Thanks everyone....
Senior Member
Joined: Aug 2014
Posts: 337
Likes: 20
From: Charlotte, NC
2005 E320 CDI, 2015 GLA 250
You should be able to measure where the current is going. If it is not going out thru the fuses then measure on the alternator wire (voltage regulator) or the starter.
Draining a battery is tough on it and worse on an old battery. 1.5 amps is a lot of drainage to deal with. Is anything getting hot?
Most car systems run at 13.5volts so 12.2 is getting pretty low.
I had a 300TE that drained out thru a CD changer but only 250mA. If left for several days, it would run down and not start. I just unplugged it when I left it at an airport or anytime for a long park.
Good luck,
Peter
Draining a battery is tough on it and worse on an old battery. 1.5 amps is a lot of drainage to deal with. Is anything getting hot?
Most car systems run at 13.5volts so 12.2 is getting pretty low.
I had a 300TE that drained out thru a CD changer but only 250mA. If left for several days, it would run down and not start. I just unplugged it when I left it at an airport or anytime for a long park.
Good luck,
Peter
Thread Starter
Newbie
Joined: Aug 2015
Posts: 8
Likes: 0
From: Monterey, CA
W211 E320
Thanks. Seems like the voltage regulator was the problem, I unplugged it from the back of the alternator and the amp draw immediately dropped. I had it swapped out and the battery no longer drains overnight!
