Hey guys,

I've searched and searched and searched and I cannot find the answer to this question.

I have a 2010 SL63 that I am storing during the winter. It has a starter and accessory battery. Do I have to keep both batteries on a charger?

The mercedes dealer tech said I just hook up my charger to the trunk battery, however, after 2 weeks of doing that my starter battery discharged and the car wouldn't start. So I switched the charger to my starter battery. The car starts now but the accessories don't all work (roof, heated seats, etc). So should I be connecting both batteries to a charger or is there something wrong with my vehicle?

I've had both batteries replaced recently.

thank you

 

may be because they didnt make any SL63 in 10. But I think the problem may be corrected if you do a reset on the battery system. Disconnect the rear battery, leave it. Then disconnect the front battery, leave it all for a few minutes. reconnect the front, then the rear.

 

really? this would work???

 

To me there is something wrong with your car. Does your car recharge the rear battery when driving ?

Try the trick from Okbarnett, maybe it will work, otherwise make some measures :
1 - Load your starter batterie
2 - Measure the power of each batterie
3 - start the engine
4 - measure both batteries while running
5 - Go for a drive (after some time your issue with electric equipement should disappear
6 - Measure after the drive
7 - Stop the engine
8 - measure again
9 - Share the results with us.


Where did you get this info from ? Maybe it is true in the US, but not everybody on this forum is from the US

 

thank you for the prompt responses!

I live in Canada and they did make a 2010 SL63 amg.

I'm certain that my car does charge both batteries. In the non-frigid months I drive the car every couple days and I never have a problem with the batteries. Occasionally I will go for vacation and if I don't touch the car for two weeks the batteries get low and it won't start. I replaced both batteries after that happened and have not had a problem with that since.

I fear not charging the rear battery during the winter months might have damaged it and I may have to replace it when summer comes around.

I will try the battery reset tactic although I'm not sure what that will do.. never heard of that before

 

NOTE 1 : discharging a battery to a point too low will damage the battery.

NOTE 2 : SL55 AMG (I assume SL63 is the same) dual battery systems are separate (according to the wiring diagrams). You require to charge both separately (I checked that the starter voltage does not rise while charging the system/consumers battery).

NOTE 3 : when “jump-starting” only use front battery (never use rear one).

There are two batteries in the SL55 (front - starter battery only; rear - system/consumers battery used for everything else).

The starter battery is dedicated to starting the car, so depletes quite slowly and seldom requires recharging. However, the systems/accessory/consumers battery requires more frequent charging, as it continues to draw down while standing, depleting rather quickly (about 0.14 volts per day).

It appears that Mercedes-Benz split and separated the batteries, as so many people store their cars for long periods, which would have rapidly depleted the starting battery (lots of electronics in the car). These two batteries are connected through a battery control module, which regulates the charging and discharging of the two batteries, as well as handling load management. The battery control module measures the load capacity of the main battery, actual current flow to loads, and can take active measures to stabilise the electrical system. These measures include increasing idle speed, connecting the auxiliary battery to the system via a relay. or shutting off nonessential consumers through the CAN Bus. This means that, under certain electrical conditions, some electrical features may not work, while at other times they function normally".

If the car is used daily, then there are no problems, but if car left sitting for a few days or more, the system/consumers battery will be depleted with everything “off-line”, until it is driven a few miles, to recharge system. Note, main starter battery (up front) holds its charge well (as it’s only for engine starting, and quickly replaces any lost charge, as soon as it’s running).

 

Can the starter battery be eliminated somehow? My E55 doesn't need one. The space created would make for a great I?C water tank as it is higher than the I/C.

 

The SL has two batteries because it has an electrohydraulic brake system, it is needed for braking system safety. Try stopping the car with no electrics, it will convince you the two battery system is necessary for street use.

 

Thanks Tom, it seems it would be easier to move the starter battery to the trunk than installing an I/C tank there. Are the two batteries on separate circuits altogether?

 

See Geo3's post above. The systems are basically separate but interconnected by a smart controller. Obviously the power circuit does interconnect since there is only one alternator to charge both batteries. The smart controller regulates loads connected, direction and rate of power flow. It is configured to allow access to and starting the car with a dead consumer battery as long as the starter battery works (at least in the US version.) Just do not drive the car until the battery recharges and the red warning message resets if you ever use this feature. I had to start the 2005 twice this way.

 

Have two trickle chargers one for each battery and never have any problems with the batteries. Maybe overkill but at least I know they are both fully charged.

 

Same here...battery tenders.

 

Hey guys,

I know this is late but just incase it helps somebody else...

turned out my problem was that the previous owner installed a boomerang which had been malfunctioning and draining my batteries.

removed the boomerang and no problems since

 

As a follow-up...my2004 SL55 AMG would not start (even though I keep both batteries on trickle chargers and the batteries are ~4 years old). I jump started the car with a NiCad jumper and replaced the front/starter battery. Car started/ran fine BUT I had a red "battery-see workshop" light on start-up that I could by-pass by just changing the display on the speedometer.
This bothered me enough to take to my excellent independent shop which diagnosed a burned "load Separation module". He said it is caused by multiple jump starts (not the case) or trickle charging???
FYI-I have not fully investigated this yet.