Old battery was taking longer to start car and would sometimes require connecting a battery charger. My old battery tested good at Interstate, but the new one starts the car almost instantly.

Decided to try the AGM type for reduced corrosion and good cranking amps.
Purchased an Interstate H8 AGM ( 900 CA 1000 CCA ) from Costco last week. Chose Costco due to their ' no questions asked return policy '.

Not sure who makes it for Interstate, possibly Clarios that recently purchased Johnson Control's battery group. Thought it might be made by East Penn but one of their technical support persons said they don't make it for Interstate.

Pain to put in due to tight fit, weight, and fear of breaking the monovalve housing.


A BMW forum says the AGM batteries must be topped up periodically by a special charger ( CTEK/Optima/others) that will slowly take the battery back to a full charge. Supposedly it increases battery life.

Also, I found comments that the battery should be connected to the special charger that will ' recondition/desulphate ' a few times a year.

Question:

For those of you with AGM experience, do you recommend that the battery be connected every now and then to a ' special ' charger to increase battery life?

I have AGM batteries in both of the CDIs. I'd be surprised if connecting to a charger enhances battery life. But, I do end up charging mine with a CTEK charger periodically since I rotate between three cars.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

My wife’s Prius requires an AGM battery because it is located inside the passenger compartment. FWIW, I’ve never done any maintenance on it and the original one lasted 10 years

The bmw reasons for topping up with a charger is unique to some bmws only

E.g. the f10 chassis was part of the beginning of something called efficiency dymanics or something, which basically means the alternator doesnt charge the battery fully, it only tops up on deceleration etc.

This is why its necessary to code the car when a new battery is plugged in.

Newer MB's do that too.....my Metris even has an active gauge you can bring up on screen to see when its doing the charging.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Changed to AGM batteries for my '82 300D-Turbo in 2005 and haven't looked back. I bought an Optima brand AGM then, when they were made in USA, and it lasted nearly 10 years. I have been told similar things by people who sell batteries- eg, that AGM batteries don't do well in old cars like my W123 because the charging voltage isn't high enough. That was when my Optima was about 8 years old.

Bought a Group 49 DuraLast Platinum from AutoZone about 5 years ago, and it's been great. In warm weather, the car starts after 1-2 seconds of cranking the starter. I had been considering some kind of reconditioning charger for awhile. A failing alternator about a year and a half ago forced my hand- the battery was drained. I was worried that the battery had been ruined, as I had read that AGM starting batteries don't tolerate deep discharging.

Got a CTEK MUS 4.3 Test & Charge and was able to re-condition the battery, and battery has been fine for the past year and a half. Replaced the alternator. This charger also has a setting for desulfate and conditioning the battery. The CTEK instructions advise re-conditioning about once yearly. I did it a few months ago with the battery left in the car. It took about 6 hours; the desulfating/re-conditioning/charging runs automatically. It charges at voltage range of 12.7-14.4 V, and desulfates and re-conditions at up to 15.8 V.

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Marshall Welch
Seattle, WA
1982 300D-T

Years ago we in the offshore Pacific fishing industry went to gel and AGM batteries for the rapidity of charge and increased cycles. They were an expensive mistake. We found out that they require a different charging algorithm than flooded lead batteries and alternators then just killed them after a year or two. There are now smart regulators I would guess. Perhaps the AGM engineers have improved them but I would research that fact before buying them again in an old diesel. We got 3 years out of an Optima in a 2003 TDI. Waste of Money.

I use a Ctek charger to keep my AGM battery charged on my '95 E300 a few times during the winter here in OH. Apparently, they a hardy but will lose charge, especially in cold weather. The older diesel car electronics do not seem to drain them very fast.

On my 2005 E320 CDI, I leave a Ctek charger on most of the time....the newer vehicle electronics will drain the batteries faster especially when the car is not operated.

I use this model Ctek charger (get the polar model for cold climates where charging is done outside):

CTEK charger suitable for our MB diesel batteries: MUS 4.3 (MB approved)

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-- Chris

'95 E300, 216k miles, Silver Surfer
'05 E320 CDI, 138k miles
'07 S550 4matic, 69k miles

Gone but not forgotten:

'76 300D, 350k miles?, SOLD in 1995
'75 240D, 300k miles, SOLD in 1991

Finally purchased a CTEK Multi 7002 7amp max charger for the AGM battery.

It does appear to give the battery a higher charge than the alternator provides. It takes about three hours to go through a complete charging cycle even though the battery measures about 12.5 when CTEK is connected. I'll probably connect the CTEK every couple of weeks since CTEK says it will make the battery last longer.

AGM battery is even better than I expected. It twirls the starter about as fast as the boost/start setting on my old Schumacher charger. This sure helps since one or two of my glow plugs are bad.

I've been using AGM batteries for years, they are a drop in replacement for automotive applications. The AGM batteries in my w210 and 2004 BMW E46 are both nearly 8 years old, bought those two batteries in 2013, and still going strong. No special chargers or maintenance. The Autozone Platinum H8AGM battery in my w210 has a "Made in Germany" label on it, so Autozone appears to be rebranding a high-quality one at least.

I also had an Optima in my old VW TDI many years ago, it lasted 5 years in the TDI until I sold the car - but I kept the battery and moved it to a Porsche where it lived for another 5 years. Pretty impressive. I have read from multiple sources that Optima quality has gone down hill in recent years however, so I probably wouldn't buy one today.

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Current fleet:
1998 E300 turbodiesel
2008 E320 bluetec - leaky oil cooler seals replaced
2012 S350 bluetec
2014 GL350 bluetec

Sold:
1996 Passat TDI
1997 E300 diesel