AGM battery only 12.25 Volts

[Volvohead]

The big Germans can suck a battery dry in no time just sitting.

I've got a big new G49 AGM in our SL. Even went crazy and bought the Genuine MB battery -- it was within $10 of the Deka. But there's no way it will make it through the winter without a Ctek on it.

A Ctek comfort indicator plug (permanently attached for charging) will show you at a glance if the battery needs charging. Great gizmo. Got one on the R in the engine compartment. Plug the Ctek in, and it keeps the battery fresh until next season (or whenever).

An AGM is a wise option for one in the trunk, especially those that don't have a good spill drain setup (like our R129).

I prefer the flooded ones for anything in an engine compartment, though. Heat is not friendly to AGMs.

Can't beat a Deka.

 

[meep]

battery chargers with desulfation stages are a crαp shoot. desulfation requires either controlled overcharge which will also "boil" the electrolyte (BAD for gel-cells) or high frequency high voltage high current pulses into the cell. It takes weeks to revive a badly sulfated batt, but the pulse method works more safely than sustained overcharge. here's the kicker.... it's still plugged into the rest of the vehicle, and I can tell you with experience that running a true desulfator on a connected vehicle battery does not make the ecu happy. So the store-bought models, I suspect are more tame. but as you make them tame, you further reduce their effectiveness.

my desulfator runs at 1khz, spikes up to 60V @ 2-3 amps for a handful of microseconds, depending on the battery's resistance. It doesn't work in all situations.

AGM will sulfate just as easily as anything else. They can be more tolerant if they have some deeper cycle design attributes, and can be aided by the sulfate not being allowed to sluff off the plates and fall to the bottom of the casing, since the mat holds everything in place. However, since it's not flooded, IF you overcharge, especially if it's sulfated, you can form air pockets inside the porous plates that might not ever refill with electrolyte, thus losing capacity. Hence why there are specific deep-charging requirements for AGM. Never bulk-charge an AGM above its rating.

 

[JHZR2]

Originally Posted By: meep
Never bulk-charge an AGM above its rating.


Great post! Good info about desulfation circuits and all.


Just one comment based upon above - some of the fastect charge lead batteries are AGM!

 

[Volvohead]

Originally Posted By: meep
I can tell you with experience that running a true desulfator on a connected vehicle battery does not make the ecu happy.


I agree. Any battery reconditioning procedures need to be taken disconnected from the vehicle. Too many computers aboard on the newer ones.

 

[JHZR2]

Originally Posted By: Volvohead
The big Germans can suck a battery dry in no time just sitting.



IMO this means that some modules arent going into sleep mode properly.

 

[Volvohead]

No. R129s are notorious for this behavior. Some other BMWs I'm told are too. Depends on the model. Alarms enabled only make it worse. Some didn't have an energy-conserving sleep modes. The newest ones are much better at battery conservation.

 

[meep]

Originally Posted By: Volvohead
Originally Posted By: meep
I can tell you with experience that running a true desulfator on a connected vehicle battery does not make the ecu happy.


I agree. Any battery reconditioning procedures need to be taken disconnected from the vehicle. Too many computers aboard on the newer ones.


Yes--- I ran my desulfator for 36 hrs or so while still connected to my previous jeep wk 2008. this car was truly computer-driven. When I finally needed it, it started fine and I drove out about a mile and then stopped in a parking lot. something caught my eye on the evic and I pressed a button to enter into one of the settings menus. the moment I pressed it, the engine shut down, the dash went nuts, it wouldn't restart, the security light was flashing, and the vehicle doesn't have a security system. took me a bit before I could get it started. lesson learned.