ksl55amg

I just bought a 2005 SL55AMG. I replaced the rear battery and tried using a trickle charger to keep the battery charged. I have two different brands . The C tech and a 1.5 amp trickle charger. Neither one will charge the battery. The only way it will charge is if I unhook the positive cable from the battery. The battery is dead with in one day of driving the car. Please help!!!

Tomcat SL

I have had no issues with my Schumacher brand battery tender and the back battery. Make sure the truck closes completely (with the tender charger cable running under the lip).

kbob999

Welcome to the R230 club. You will love this car once it is sorted out.

I don't think you have a battery problem, but a drain, or alternator problem.

Start the car with chargers disconnected and see what the voltage is at the rear battery. Should be close to 14 volts. If you have less, the car is not charging the battery.
Likely a regulator (~$40 DIY) or alternator (~$150 Autozone lifetime warranty). I've gone through 2 alternators and a regulator.

You can also check that all glovebox lights, dome lights, trunk lights etc are not draining the battery. Normal drain is small, but still there, as the computers monitor the systems even when off. Anything over 1/2 amp when sleeping is too high.

Let us know what you find.

ksl55amg

Thanks guys. I will check these things out and get back to you.