Out of curiosity does anyone know what the average voltage in the rear battery is?

I left for a number of days and hooked up my battery tender to the rear battery. Unfortunately, I didn't check the voltage before I left, but when I unhooked the tender and checked the voltage it measures 12.51 volts. That seem low to me, paticularly since the battery is only 3 months old.......

12.5-12.7v when off, 14.2-14.7 with the engine running.

ALX,

That is good information to have.

Thanks.......

after it sits for days, its going to show about 12v , then when you crank it it may go hi for a while till it charges back

Thanks for that information too.

I figured the battery should charge up to around 13.5 V and when it was only 12.5 V I was concerned that I had a bad battery on my hands.

So, knowing both the lower and upper voltage eases my concerns.

Because our SLs seem to be busy doing stuff that uses battery power even while resting in the garage, most of us use trickle chargers hooked to the trunk battery if the car is not going to be driven for a week or more. Mine sits all winter with trickle on it.

+1...big CTEK on the SL65 while I'm here on vacation. No issues ever since its been hooked up. Mercedes seems to over engineer everything except battery regulation and cup holders...

+1 on the big ctek- I love that charger- have three of them...

For almost the price of one (1) "Mercedes" brand trickle charger which is just a CTEK with MB logo decal...

correct. same box and same markings sans the mb logo.

ditto on porsche and bentley chargers to name a few