According to the Mercedes forum, I could check the cells and add water if needed. Well they also seemed pretty dry. This battery was made on the 38th week of 2011. Yet I think it will be restored to full function. Amazing. I added water and charged it. Reinstalled. If this really works I just saved like $200.
07 S550: service rear battery
07 S550: service rear battery
The rear battery is also the aux battery but its actual job is....everything except for cranking the engine apparently. I removed it which was a little involved. In fact with the battery out the car was totally dead. I had a mini-freakout when I closed the trunk because it wouldn't pop open. Remembered the key fob has an emergency key and there is a lock cylinder sort of hidden above the license plate so I got it open.
According to the Mercedes forum, I could check the cells and add water if needed. Well they also seemed pretty dry. This battery was made on the 38th week of 2011. Yet I think it will be restored to full function. Amazing. I added water and charged it. Reinstalled. If this really works I just saved like $200.
According to the Mercedes forum, I could check the cells and add water if needed. Well they also seemed pretty dry. This battery was made on the 38th week of 2011. Yet I think it will be restored to full function. Amazing. I added water and charged it. Reinstalled. If this really works I just saved like $200.
Re: 07 S550: service rear battery
Apparently the restoration of capacity could take months....
As of now I don't think this has meaningfully improved. I am still seeing wonky dome light behavior. Unfortunately the battery is very difficult to access so it is not easy to just check the voltage.
As of now I don't think this has meaningfully improved. I am still seeing wonky dome light behavior. Unfortunately the battery is very difficult to access so it is not easy to just check the voltage.
Re: 07 S550: service rear battery
I plugged in the built in Napa charger. I'll do that for a while and see if that helps the process.
Re: 07 S550: service rear battery
Turns out I overfilled the cells because I was being lazy and didn't want to have to check on the battery monthly. Plus I was trying to ready the car for the FL trip. 10 months later and I decided to pull the battery out to check the levels. There was battery acid all over everything. Shit. I must have used almost a gallon of baking soda solution and 25 large shop towels to soak everything up. There is permanent corrosion in places, and discolored metal/materials in other places. I think it ate the galvanized coating on one of the rear SAM brackets. There are electronics all over the place back there and I had to remove all trunk liners to rinse and clean everything. It sucked.
In the end I bought a Diehard from Advance Auto (had several in stock, 7/22 date). It's a slight upgrade over factory with 900CCA and 170 minutes reserve time. Pretty stout. Group 49/H8 I guess they call it. $246 or so after core and taxes.
Lesson learned?
I decided to remove the Napa charger that the PO installed, now that I know you can charge the rear battery from a terminal in the front. So handy. Charged it overnight and it should be good to go now. When checking the old battery it was like 11.8V after just opening the car and that rose to low 12s after some stuff stopped drawing. Hopefully this one holds up much better. Again, no real symptoms other than dome lights that cut off seemingly randomly. That, and if I were to have a phone call after shutting the engine off, I would get a low battery warning after 5-10 minutes. But with the dedicated starting battery, none of that really mattered much. At least it should be 100% now.
In the end I bought a Diehard from Advance Auto (had several in stock, 7/22 date). It's a slight upgrade over factory with 900CCA and 170 minutes reserve time. Pretty stout. Group 49/H8 I guess they call it. $246 or so after core and taxes.
Lesson learned?
I decided to remove the Napa charger that the PO installed, now that I know you can charge the rear battery from a terminal in the front. So handy. Charged it overnight and it should be good to go now. When checking the old battery it was like 11.8V after just opening the car and that rose to low 12s after some stuff stopped drawing. Hopefully this one holds up much better. Again, no real symptoms other than dome lights that cut off seemingly randomly. That, and if I were to have a phone call after shutting the engine off, I would get a low battery warning after 5-10 minutes. But with the dedicated starting battery, none of that really mattered much. At least it should be 100% now.