Battery Disconnect

[darrin]

Originally Posted by Schulisco

I have to admit that I don't know a solution for you. But I do not get why people use an AGM battery in vintage cars...IMO completely senseless unless you modify the alternator to increase the voltage. Even then still no benefits due to absence of start stop systems. I doubt that they will last longer or bring other benefits like weight saving.
Any way everybody's own decision...

Thomas

Thomas, after having a failed voltage regulator cause my wet cell battery to boil over, requiring me to fix damage to the battery tray area, I switched to an AGM, as it's my understanding that an AGM battery's glass matt encapsulation design/construction makes it much less susceptible to boiling over and damaging surrounding areas of the car. It's been close to 30 years since I made the switch and I'm on my 3rd AGM battery, without modifications to my voltage regulator / alternator and with only occasional use of my CTEK smart charger (only use it to run a recharge cycle if I haven't driven the car in over a month). FWIW

[wazzz]

Not defending the AGM batteries here (as I also keep my heavy lead-acid battery in my 911), but I think the requirement for a higher voltage is mostly relevant in modern car applications with start-stop technology. Because of the higher demand for electric power in these cars, the battery needs to be charged more quickly than in standard applications, hence the higher 14.7V regulator.
The higher the charging voltage, the higher the charging current and the lower the time required to reach full charge.
But in an air-cooled 911 without start-stop, the AGM will be less loaded and because of the lower demand, it will have more time to charge despite the lower 14.3V regulator. A 12V (or 12.8V) battery will get fully charged provided that the charging voltage is higher than its nominal voltage. It is only a matter of time.

[mysocal911]

Originally Posted by Schulisco

I have to admit that I don't know a solution for you. But I do not get why people use an AGM battery in vintage cars...IMO completely senseless unless you modify the alternator to increase the voltage. Even then still no benefits due to absence of start stop systems. I doubt that they will last longer or bring other benefits like weight saving.
Any way everybody's own decision...

Thomas

Totally agree! It's laughable people waste money on a switch to an AGM, especially where the alternator's output is on the lowside, e.g. 964/993 Bosch alt @ 13.5V.

[911 Rod]

Originally Posted by mysocal911

Totally agree! It's laughable people waste money on a switch to an AGM, especially where the alternator's output is on the lowside, e.g. 964/993 Bosch alt @ 13.5V.

We do it because the proper size battery is massive!

[Schulisco]

Darrin,
I don't doubt your experience. I had a competely controversial experience on a car which I had before the 911 as "toy car", a 2004 Audi allroad with the 4.2 V8... Unless you drive long distances the battery wouldn't get fully charged. The AGM was recommended by Audi itself for that car, but in the retrospective I'm convinced that the alternator and the board system weren't prepared on that. So I had to replace the battery a second time short period after. And then I switched back to a conventional.lead acid. No further isuues any more.

Times may have changed now and the AGM are now of better qualty. I could find sources on the net saying that they won't spill as the system is fully enclosed and due to the absorbant glass matts it will reuse the water/hydrogen again. I doubt that they will never explode but I believe that the operating security is higher than conventional.batteries. I agree with Gilles that they're mainly intended for modern cars with much more electrical stuff on board together with the presence of start stop systems. The higher voltage is due to the AGM technology afaik, a welcoming side effect ist the quicker charging as Gilles already explained. But again - the board system must deliver this higher voltage too.

All things we don't have in a the old 911. I prefer to stay with the old lead acid batteries and from time to time I check the voltage of the system either with a cheap 10$ chinese multimeter I carry within the 911 or with a cigarette lighter plug and voltage display in the glove box.

When the car is parked in the garage I switch of the battery from the car with a cheap battery saver switch like these:



Every 1-2 months I recharge it when haven't been driven since. My dad already could keep car batteries much longer than ten years in his cars that way...I continue that.

[creaturecat]

in addition? a voltmeter plugged into the cancer stick igniter is money well spent. order a Euro unit, if you don't want to shim (etc) the voltmeter in place.

[ChrisHoover]

Was your car repainted? I found the grommets were gone and the conductors had worn through the insulation shorting to the body. I measured current from the fuse block to locate the faulty conductor

[Mark Salvetti]

Originally Posted by 911 Rod

We do it because the proper size battery is massive!

FYI there are two group sizes that fit. The huge one is Group 49/H8. The smaller Group 48/H6 will also fit. There is a second hole for the battery hold down.

Mark

[pmax]

Originally Posted by mysocal911

Totally agree! It's laughable people waste money on a switch to an AGM, especially where the alternator's output is on the lowside, e.g. 964/993 Bosch alt @ 13.5V.

Laughable ?

I gladly pay more for a battery than paying a lot more when the battery spews acid.