DRK1

2003 SL500. New battery in trunk goes down when car is not driven for weeks. Is there a source of battery drain when everything is off ? No problem with starting battery. Thinking I made need a battery maintainer for this battery.

cdk4219

Yes you do, there are a few things that will drain the battery, one being the vacuum assist pump that leaks. Regardless the Band aid is a good battery maintainer.

A1EK

The car should be able to work after a few weeks of not being used. You may get the message convenience functions off line on dash, but it will clear once the battery charges a little after 10 mins. I would recommend using a genuine Mercedes dealer battery, they are the best I have experienced. Good luck

jcollins133

Above 2 answers are right. It's a common problem. If I am going to leave my SL500 for more than 3 days, I hook it up to a battery slow charger (Mercedes charger). No big deal so long as I don't drive off with it still attached to the battery. (me)
Before you get a new battery, have the existing one checked. You can always drive off and it will charge up within minutes (Just can't hear radio or lower top, etc.)
You might google battery failure or similar term. I recall seeing a YouTube on this exact problem and some ways to stop it or at least reduce it.
Good Luck. It's a great car.

Bdevil82

This guy puts a charger on both batteries. I had always heard if you just do the consumer battery, it would feed the starter battery:

g0rsq

Thats because he can sell twice as many "battery tenders"

Only need one on rear battery, though I would chase down as many parasitic drains before using one.

If you have more than about 200mA parasitic drain, you have a problem that needs sorting before relying on a battery tender!!

Car should start after at least 3 weeks of non use without consumer offline warnings.

jcollins133

Try this:

cdk4219

You can do the same thing with the multimeter in the picture. I dont see any advantage to this at all. Plus this just tests the drain at the battery, doesn’t help find the culprit at all. Unless I am missing something with the lisle contraption.