Nothing is currently dead or dying, but soon I will be buying a new battery. Sears battery selector is saying I need a 94R, pretty sure it has a group 49 in it now (US 83).

While I am snooping around looking at brands and group sizes I notice in the Bimmer forum that people are saying an AGM battery requires some change to the engine computer to keep the voltage below 13.5v (or something like that).

Whats with the group size 94R?

Do we need to worry about our charging systems running at 14.5v with AGM batteries?

 

The engine computer has nothing to do with the charging voltage - only the voltage regulator on the alternator sets that. In general AGM batteries seem to do OK when using the same charging system designed for a wet cell - though it may not be optimum.

However don't convert to AGM unless you have other reasons - ignore the Sears selector (nothing changed on your car....only their selector) - if they don't have the battery you want go elsewhere: early cars Group 49, later cars Group 48 ... why do different?

Alan

 

Late model BMW's are very picky on what battery is used in them. Their electronics are far more complex than any 928 ever.

 

Can't say anything about AGM batteries but if you have an Interstate near by, their batteries are pretty good. Same with the Wal-Mart Everstart Maxx, which would be cheaper. I run an Everstart in mine after the Energizer battery was getting a little weak (which lasted almost a decade, including a 3 year sit, surprisingly). My dad's 911 has a new Interstate (Porsche batteries really do suck).

 

AGM batteries work really well also on standard 928, PO left me the AGM battery in the GTS, it's now 7 y ears old, with battery tender I think it will last about 3-4 years , on my daily driver, a pt cruiser diesel, the AGM battery is 11,5 years old and it's still going well, despite the last winter it was weak.
but hey, it' s +11 years old.

 

I have one agm battery in a 1990 p'kup. I also have a charger for afm batteries. What I noticed between agm and regular battery is initial charge from charger will leave agm at 13.5 volt. Regular battery is 12.5. The p'kup charges at over 14 volt so battery stays full charged.

I used this battery in one of the porsches but eventually sitting state (after a week) was 12.5 volt. It always cranked like a demon, but never achieved the 13+ sitting voltage as when on the p'kup.

Just my observation, not scientific, but may be why agm not needed/desired for 928.

 

Bosch battery from PepBoys, three yr free replacement & 5 yrs prorated. Hope I don't have to test the 3 yr portion.

No more WalMart EverStart Maxx or Auto Zone batteries for me. My experience with both in recent years on other vehicles in trying to get a "free" replacement wasn't worth the hassles. Big change with both their policies from past years. One died in my truck this past yr & Wally World kept saying the battery was good when it wouldn't hold a charge. Ended up just getting a maintenance free one from NAPA. That $85 EverStart was an expense two yr battery.

 

True on the 928, but many "modern" cars like my 99 Lincoln Continental the ECU controls the alternator, provides the input to the regulation control instead of a passive circuit.

Pep Boys and Bosch or Energizer went in for several years, then a AutoZone Duralast, but none lasted all that long. Now both cars have a battery cutoff switch and I used it anytime the cars are parked for more than 12 hours or so. Unfortunately this seems to keep a half dead battery still functional until its totally dead.

Not easy to tote around, but I have a spare battery waiting to be a core, so whatever I buy is going to sit side by side with it and better be the same size, group 49.

No special reason on wanting AGM except the normal Porsche sickness of wanting whatever is "best".

 

I think the main issue with modern cars isn't the ECU regulation per say, but enhanced output on a modern alternator vs old style that "cough cough" puts out 14.5v as long as the moon is full and headlights aren't on, etc.

 

Will an Optima yellow top work fine in an 87?

 

I've always heard very mixed revues on the Optima, expensive too.

 

Yeah they are pricy, however I have an extra one on the shelf that I was thinking about putting in. I was thinking of adding it for an upgraded stereo system im putting in this winter

 

6 months, no problems. i got mine at advanced. mine was an AGM, direct fit. not like the Gel cells....

 

Jake

Which battery you speaking of?

Thx

 

^^^ This one, I think.



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