El Cid

I had posted another thread on specific battery issue, but wanted to start a new thread based on new information from dealership.
One employee told me that letting the car run in idle (parked) will do nothing to recharge the battery, no matter how long you let it run. It can only be recharged if you drive for 20 miles or more as the alternator does not work in idle. 20 miles results in a full charge.
Another employee said that letting it run for two hours after jump starting will result in a good charge.
Who do you believe? Both were in the service department.

KEY08

Unless the alternator has a clutch mechanism it should be spinning anytime the car is running. If it is not charging then there should be a warning not to sit in your car with it running for extended periods of time. If you are sitting and waiting for someone or whatever, your car will surely die working off of battery power only.

thefisch

Not to be dramatic, but I wouldn't believe either of them. Idling you car for 2 hours seems like an expensive, time-consuming and environmentally bad substitute for a trickle charger. While going for a long drive (20 miles) has been conventional advice for recharging a battery, I have done that before with a dying battery in my 2011 only to have it not start the next morning.

There was a post a while back on the variable charging logic for the W212 that in a nutshell showed that the car decides what output is needed from the alternator based on a number of factors. It isn't one size fits all. I would only trust my Ctek charger and multimeter to verify.

mellonc

Trickle charger is the answer here. I picked up mine from an auto parts store for $30. yellow light for charging and green light for fully charged. simple.