gronk

Greetings: Recently had red battery symbol on display "visit workshop". All vehicle function working. Can't reset using onboard menus. Dealer diagnosed as failed gel bty in engine compartment. Veh had been serviced prior for SBC and volt regulator recalls. Could this situation have been triggered by 2A trickle charge applied to main bty in trunk. If so, how does one safely recharge main bty after long period (say 2 months) of nonuse? Thanx!

DWP

Accidently ran down main battery by leaving headlights on. Disconnected both battery leads (though probably OK to leave negative lead connected) and applied trickle charger to battery. Charged for 4-6 hours until charge rate declined to 50% of original rate, disconnected charger, reconnected battery leads. No negative consequences noted from trickle charge of battery.

sl561

x

billh556

That's interesting.... if you leave the headlights on, they don't eventually shut off on their own? I mean not on auto, but manually turned on (full right on the switch)? I would have guessed the electrical system would shut down everything after some amount of time after engine off... I had a BMW that did that - everything off after 20 or 30 minutes, inside and outside lights included.

Learn something new all the time on this forum!

Otto

I use a trickle charger without problem. Please make sure your trickle charger stops charging batteries automatically which it finishes. (check battery tender out, you may need a "international" one for Hong Kong.)

SAguirre

I always use a trickle charger, it is a really a float charger or something like that. I think that it charges at 1.5 amps and then stops charging at a particular voltage. When the battery voltage drops again, it starts to trickle charge again. I have been using it for 1 year on this car and it has been connected for about 7 weeks (the amount of time the car sits unused). I have never had any problem and my dealer said it was fine to use it.

Mercedes even sells a trickle charger that is ancient in design and will NOT stop charging the battery when it is full, so I don't think that you could have caused any of this with your charger. However, there is a chance that you ensured that the main battery in the trunk was not drained and that is why your car worked fine in spite of having a faulty battery under the hood.

Who knows?

Steve

DWP

I would have guessed it too, but I would have guessed wrong. The car will turn off the radio if it's on without the key after 30 minutes or so, but it will leave the headlights on without the key until the battery is drained. One theory offered in a previous thread to explain this "Dead Battery for Dummies" (like me) feature is that if the car plunged into a canyon at night, and the engine stopped running, potential rescuers would still see the lights. Or something like that. Anyway, it's good to know that thoughtful M-B won't let me drain the battery by leaving the radio running for several days unattended.

CE750

Yeah the W211 electrical system as a pretty advanced load shed system for when the batt gets low.. I read about it in a maintenance manual a while back at the dealer... there are several buses and they are shed as voltage drops.. lights aren't on it, since Auto is your idiot proof system for that, and if someone has the lights in "on" they are assumed to specifically want them ON.