Issues with Bosch AGM?

Was wondering if anyone has ever experienced odd longevity issues with Bosch AGMs. I got the Group 49 (big one) for a Gwagen diesel which is the stock size.

It worked great for about a year and a half. My starting speed became really slow over about a month of off and on driving. I thoroughly checked for parasitic drain, alternator issues, etc.. I monitor voltage in real time too with a dash gauge and it's always 13.5+ while running so it's not an electrical issue with the truck.

This was further proven after I took it back for a warranty replacement which Pep-boys did after putting it on their tester and agreeing it was "off". The new one solved the problem, until last month when the same thing started happening. I even had a Battery Tender hooked up to it full time. It's fine coming off the charger and when starting up after driving, but if you leave the stereo on for just 10 minutes or don't drive it for a few days, it's back to barely starting. The warranty won't cover another replacement so I'm basically out $200.


There is extensive info here about the Odyssey/former Die Hard Platinum Group 31 battery needing a higher charging voltage than most other batteries, and higher than most common vehicles supply. I don't know what size your Group 49 is, but is it possible that the Bosch Group 49 AGM has a similar issue with charging voltage?


Engineer In Residence
Are you checking voltage at the battery itself? A higher resistance on the alternator to battery path could easily cause undercharging and death. 13.5V is a bit low, 13.8V would be the minimum (obviously vehicle dependent). I have seen occasions where a voltage drop in the wiring results in a abnormally high voltage at the battery, but normal-ish voltage at the vehicle modules.

What voltage does your battery tender run at? An abnormal high float voltage from the tender could cause early death.

Last I heard Exide was making the bosch branded batteries.

Some AGM batteries recommend a higher finishing voltage (14.6v). Even when used for light starting duty, they can sulfate without the occasional absorb charge at higher voltages.

Finally, what is the manufacture date on the battery? If it was sitting on the shelf for a year or more, it may have been badly sulfated before you even got it!

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Higher voltage needed for sure. See if the VR can be adjusted up.

Or go FLA, much more robust.

Last option, put the replacement batt on a decent mains charger a couple nights per week.
Voltage goes above the 13.5 but isn't hitting over 14.1 much. I checked the gauge against an on-battery test with a Fluke meter and it was within .1v. Can't adjust the VR (nor has it needed adjustment since 1979 when it was built!) Of course it only ran FLA's.

The tender seems to float it around 13.5-14 depending on the cycle its on. The tech at the factory said it was the correct tender for the battery after a long call with them. Bosches, like most, aren't "thin-plate pure lead" so typical Tenders service them fine, according to him. Higher-end AGM's need an AGM tender. This was bought recently as well so the issue isn't there.

The manf. date was only 3 months before I bought it.

Regardless, if these AGM's are going to be this finicky, I'm done with them. I had a Red Top many years ago on an old Land Rover and it never impressed me with either longevity nor recovery after winching. I mount conventionally anyway so why bother. The best battery I ever had was actually a big old fashioned Interstate.

So the new question, based on what's available to me for a good price, Duracell Ultra Gold or a Super Start Extreme? I assume both are Deka's. They both have the same body from looking at pics. The specs are real close, though the Duracell weighs 2 more lbs. 1100CA with 185RMin. which sounds pretty nice for my diesel.
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Thanks. Went with a Duracell today. Batteries Plus had a deal. Date sticker is 2 months old. Very helpful staff who insisted on carrying it to my car, and carrying in my core.

I learned that BP calls their "advanced" Duracells "Ultra Golds".

With discount, core refund, plus tax, a big group 49 was only $145. The starter spins 2 times faster now! Time will tell the rest...