auxillary battery replacement ---Help
 

Is there a DIY on aux battery replacement on the 2003 sl500? need to replace and don't know where to start or even where it is on this new to me body style
thanks
joel

Here's one. I'm sure location varies but it's your car -- look around. :D

DIY - Auxiliary Battery - MBWorld.org Forums

The starter battery is under the hood. The systems battery is in the trunk.

so is the auxillary battery the systems battery?

The R230 doesn't use an auxiliary battery. The little battery under the hood is only used to crank the engine. The big battery in the trunk does everything else.

sorry for my density here. my car cranks but key fob doesn't unlock carso which battery is that?

The big one in the trunk.

The two in the key.

Which vehicle are you referring to?

My 211.026 is the reverse. The group 49 cinderblock is in the trunk adjacent to the spare tire and battery control modules

The 211 541 00 01 ATV/motorcycle/PWC size computer systems battery is under the cabin air filter behind the right shock tower next to the washer reservoir.

The R230 and W211 both use two batteries, but for different reasons.

As previously posted, the R230 uses the little battery under the hood only to crank the engine. The big battery in the trunk does everything else.

The W211 uses the little battery for back-up power for the SBC brakes. I know, both cars have SBC brakes, so why would one model have a back-up battery for SBC and the other one doesn't??? Ya' got me! I'm sure the MB engineers had a good reason, though. :)

Back up battery.
 

SBC can be a repetitive drain on the battery when parked, leaving you unable to start car. The 211 gets by with the small battery. The SL needs more juice to power the top, rollbar, ABC etc. so it needs the larger trunk battery which often runs flat after several days. However car starts just fine on the front battery.