Second Battery - Mercedes-Benz Forum
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post #1 of 6 (permalink) Old 10-25-2012, 01:47 PM Thread Starter
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Second Battery

Hi All,

Does the second battery get any charging when the car is running?

I routinely hook up my trickle charger (1.25 amp) and it soaks for two or three days to bring the second battery to "full charge". I thought it was because my SL was a victim of short trips. But.......I just returned from 500 mile Interstae trip and same deal...took a two day trickle soak.

If this is normal...fine. If not, perhaps it's a cuurent drain.

Comments please.

Thx, Don
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post #2 of 6 (permalink) Old 11-27-2012, 11:35 AM
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Hi Don,
I've had the same experience. What you refer to as the second battery (in trunk) is actually the main vehicle battery. I'm sure that it gets charged (I've measured the voltage) when the engine is running.
Don't know why it still takes a charge after a long run. I did read somewhere that there are vehicle systems that are constantly drawing current, even with everything off and locked. Perhaps that is the cause.
Take care,
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post #3 of 6 (permalink) Old 12-05-2012, 06:33 PM
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the venicle is very smart, it only uses the starter battery for starting, and only charges the starter battery when it needs to. dont be alarmed.. just drive and be happy!
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post #4 of 6 (permalink) Old 12-27-2012, 11:41 AM
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Originally Posted by eckerson89 View Post
Hi All,

Does the second battery get any charging when the car is running?

Comments please.

Thx, Don
Yes, just like the R230 SL....

Horsepower: enough power to go from point A to point B
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0-1/4 mile: about 5 minutes @ 2mph because no need to showoff

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post #5 of 6 (permalink) Old 05-15-2013, 07:14 AM
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Second battery

Found the main battery in the trunk but I'm told by the Dealer that the smaller battery, which needs occasional charging, is somewhere under the passengers seat. I can't find it! I'm told that should it have to be replaced the car has to go to the Dealer where it takes about 2 hours to swap the old for the new. At $125/hour plus the cost of a new Mercedes battery that should come to about $500

Does anyone know where to get a look at a shop manual?
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post #6 of 6 (permalink) Old 05-15-2013, 11:40 AM
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Smaller battery sits in a compartment behind passenger seat under removeable lid.
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