Battery surprise...

[Greg D.]

Last year I bought 2x Sonnenschein batteries for the 72T. Those set me back an arm, a leg and a kidney, but came with lots of recommendations on the forum for fitment and quality. The date engraved on them was 10/12 but I used them starting end of 2013. They have a year on the car, give or take..

I drove the car last about 3 weeks ago, nothing was left "on"... Today the car was dead as a doorknob. Get this: 0.5V at both batteries... I struggle to explain this, as the car has been great on battery drain (none) for the past years and never before needed to be on a maintainer. The only thing that changed is we've just had a cold snap the past few days (not quite freezing, but pretty close, 36F at dawn outside) and the garage is not insulated... That said, my 912 that sits right next to the 911T started with 12.6V today, happy as can be... With a generic battery to boot, not an expensive gel sonnencheim ! Anyway, I'm putting both on chargers/maintainers - but don't know the inners working of those things. Do you think the odds of reviving gel batteries that went down to 0.5V are good or did they suffer too much ? Any tests I should do to know for sure? So far they seem to take a charge, no warnings on the charger, I used the lowest setting on the charger to be gentle (2A instead of 12).

*If* they won't take a full charge - or keep it, I'm leaning towards sideways Miata/Westco because even these "perfect Sonnencheisse"(!) positive posts are awfully close to the battery box, IMO...Still I'm curious, the car has lived in warm climates the past 20yrs, but I've never seen a such a drain in 3 weeks unless you leave the headlights on or something... Can it really be the cold on a 2y old unit? If so I'd think the 912 one would have died sooner, it's older, single battery, while those 2 were paired and much fresher... Odd...

[drwhosc]

If you don't drive frequently, trickle charge is your friend. Mine will not hold a charge either. Batteries don't last long either...

[Greg D.]

If you don't drive frequently, trickle charge is your friend. Mine will not hold a charge either. Batteries don't last long either...

Oh, for sure... But I've left that car undriven on occasion and the voltage hardly dropped... I'm surprised - Low 12s I'd understand, but 0.5V, yikes... Must be another factor, the cold maybe. I hope I can revive those things, I'm certainly not buying that brand again regardless - too pricey, tight fit. Especially when the older "el cheapo" battery 6ft away was A-OK! I was hoping someone might chime in with tips for safe revival, but it's the holidays, nobody's on the forums ;-) I'll leave them on the charger and see...

[SIMI BOB]

My daily driven C230 MB has had the same battery for 14 years. Garaged every night in So Cal. Don't know what the secret is, but that's the longest lasting battery that I have ever had.
Bob B

[edmayo]

Last year I bought 2x Sonnenschein batteries for the 72T. Those set me back an arm, a leg and a kidney, but came with lots of recommendations on the forum for fitment and quality. The date engraved on them was 10/12 but I used them starting end of 2013. They have a year on the car, give or take..

I drove the car last about 3 weeks ago, nothing was left "on"... Today the car was dead as a doorknob. Get this: 0.5V at both batteries... I struggle to explain this, as the car has been great on battery drain (none) for the past years and never before needed to be on a maintainer. The only thing that changed is we've just had a cold snap the past few days (not quite freezing, but pretty close, 36F at dawn outside) and the garage is not insulated... That said, my 912 that sits right next to the 911T started with 12.6V today, happy as can be... With a generic battery to boot, not an expensive gel sonnencheim ! Anyway, I'm putting both on chargers/maintainers - but don't know the inners working of those things. Do you think the odds of reviving gel batteries that went down to 0.5V are good or did they suffer too much ? Any tests I should do to know for sure? So far they seem to take a charge, no warnings on the charger, I used the lowest setting on the charger to be gentle (2A instead of 12).

*If* they won't take a full charge - or keep it, I'm leaning towards sideways Miata/Westco because even these "perfect Sonnencheisse"(!) positive posts are awfully close to the battery box, IMO...Still I'm curious, the car has lived in warm climates the past 20yrs, but I've never seen a such a drain in 3 weeks unless you leave the headlights on or something... Can it really be the cold on a 2y old unit? If so I'd think the 912 one would have died sooner, it's older, single battery, while those 2 were paired and much fresher... Odd...

Greg, I don't know where you live, or how cold is 'cold' but I have three cars with Sonnenscheins and I've never seen such a problem due to the cold here in Fort Worth. (we will sometimes sink to the twenties when a front comes through) On my daily driver 71 I recently had to replace the Sonnenscheins after 8 years of use. As to the positive post are you not using the molded rubber cap that is supposed to go on the positive post? Absolutely prevents post from touching anything. They might still be available new, or search swap meets.


Be sure to check dome lights and light under glove box to be sure they aren't on.

[Frank Beck]

My daily driven C230 MB has had the same battery for 14 years. Garaged every night in So Cal. Don't know what the secret is, but that's the longest lasting battery that I have ever had.
Bob B

You would be wise to replace it today.

And then forward your old one to the Smithsonian.

[Greg D.]

Well as of this morning they're both back over 13 V but not lighting up the "fully charged" indicator on the maintainer yet... I realize this isn't a fascinating topic, I just hope I didn't miss the right way to resurrect gel batteries. We'll see. I'm also eager to plug them in and triple check whatever drains there might be, because I'm positive (ha) nothing was left on. The only work I did was putting rear belts in the car upon return from Easy. So maybe one hour of door light, max.

Edit: topped off, green light... Took 14 hours !!! I truly dislike double battery systems, I always forget once you connect one the system is live and I always spark the other + cable on something accidentally... Ugh !! Anyway no harm done. The car starts, runs, no alternator light, and there was indeed nothing left ON. Still baffled. I'll try and troubleshoot drains that weren't there before, or just leave it on the maintainer because it's damn cold ;-) Fingers crossed they remain good!

[RSTarga]

Get a charger/maintainer that automatically recognizes charge level and type of battery. Gel batteries are easy to destroy.
On a side note, I was in a Pep boys the other day and saw these Bosch batteries, they fit perfectly into the battery box in the normal upright position. Anybody here think they would make a good substitution? They are 125 each, are the Sonnencheins much more?

[Greg D.]

Get a charger/maintainer that automatically recognizes charge level and type of battery. Gel batteries are easy to destroy.
On a side note, I was in a Pep boys the other day and saw these Bosch batteries, they fit perfectly into the battery box in the normal upright position. Anybody here think they would make a good substitution? They are 125 each, are the Sonnencheins much more?

That's about 1/2 the sonnenscheins - so yeah, if you can catch a ref# next time...

[RSTarga]

If you can see the lower picture it has Sku and part number. I think these must be the Miata type battery. Size U1