Still questioning about batteries - why not to go with standard ?

[fizeus]

Hi all,
I'm reading a lot on this forum and I see many users are repositioning batteries.

Recent post remembered me I'm running with 10 years old batteries so it's probably time to replace mine with new ones.
I think it's not an urgent job cause mine seems to still perform well (i usually unplug batteries when I park the car)... i'm planning the job.

Today I've found two perfectly fitting batteries for my 73... those batteries (Banner Batterien) are about 73Ah each and reading at specs my 911 just need two batteries with 36Ah each.

Using two Bannerbatterien.com batteries (model 572 12, B13 mount, 72Ah, 650Ah Peak) will end up with 146Ah of total capacity.

Question: can this cause problem (wear) to the alternator ?

While I fully understand the reason to replace two batteries with just one on a racing car (weight reduction) i cant understand the reason of this re-positioning battery trend.
Can anyone please tell the reason for re-positioning batteries and switching from a two batteries configuration to a single battery advantage.

I'd like to keep as stock as possible ... but I don't want to cause damage or problems to the alternator or other electrical components (like voltage regulator).

Can you please comment or post your opinion ?

Here is the link for the battery http://www.bannerbatterien.com/backend/datasheets/EN/010572120101.pdf

[Rawknees'Turbo]

The smaller batteries actually put less wear and tear on alternators as it takes much less juice to keep them charged (less "work" is asked of the alternator).

[Porboynz]

If you start with fully charged batteries then the alternator load is the same to replenish whatever capacity was used during starting, so IMO the larger battery capacity is a good thing that reflects improved technology since the originals were specified. (But avoid the so called calcium/calcium batteries as I understand they need a slightly higher charge voltage than an older 911 is designed to produce)

[grizzfan]

Since the Banner brand batteries don't appear to be available in the USA, I presume from your post that you don't live in the US.

Were I to replace my two batteries in my 1973 I'd be looking for the AGM type battery. They are practically leak-proof. The Mazda Miata battery is an exact fit and is AGM (acid glass mat). So, check out a Mazda dealer where you live.

Best,

Tom

[fizeus]

thank you all for you replies, still a lot of think to learn about Porsches.

For what I understand it's better to use just one battery than two, at least in this case.
Is there any problem if I use only one (73Ah) battery?

I assume also I have to triple check that second battery cable is fully isolated to avoid accidental contacts with any metal part of the car (ground).

And unfortunately Mazda-Miata aren't available from my local dealer, in Italy. :-)

[Brorag]

remember the front end is light--batteries add needed weight to the front end.

[grizzfan]

fizeus posted:

For what I understand it's better to use just one battery than two, at least in this case. Is there any problem if I use only one (73Ah) battery?

My understanding is that the very exacting Porsche engineers wanted to ensure weight balance in the early cars and made arrangements for one battery on each side to achieve that. I have never heard that one was better than two. When I purchased my '73 911T six years ago it had one battery, not of the stock size, wedged in between the fender and spare tire - not a good arrangement at all. The other cable set was wrapped in plastic. I decided to go with two batteries as intended by our German friends. Car runs just the same.

Be certain to go overboard in isolating the spare set of cables if you decide to go with one battery as the spare set is very close to the gas tank!!

My recommendation is to go with two batteries and see if you can find the AGM type in Italy. There must be a manufacture in Europe somewhere.

Best,

Tom

[RSTarga]

I've got two Miata AGM's. Putting a lead acid in will lead to rusting of the front suspension pan. If you live in Europe Sonnenchein makes an exact fit in AGM for dual batteries.
If you decide on one battery, don't insulate the pass side cables, disconnect the hot lead at the drivers side. Much safer.

[911pcars]

Originally Posted by RSTarga

I've got two Miata AGM's. Putting a lead acid in will lead to rusting of the front suspension pan. If you live in Europe Sonnenchein makes an exact fit in AGM for dual batteries.
If you decide on one battery, don't insulate the pass side cables, disconnect the hot lead at the drivers side. Much safer.

Using a non-venting AGM battery (no acid vapors) should be reason number 1.

Sherwood

[HarryD]

I went with a single Optima.

This thread has a good discussion:
duel battries

My thoughts are:

Sonnenschein is the way to go to keep the factory set up. You will need their DF75 (A512 /40 A) gel cells - Wholesale Battery Distributor - Retail Battery Distributor.

An alternative is go with a single Optima on it's side in one of the boxes and disconnect the excess wire.

Also, you can get the exact fit lead acid style ones from your Porsche dealer (New Editions - Classic Genuine Parts & Literature - Porsche Classic - Dr. Ing. h.c. F. Porsche AG). Look for: "Battery 12V 36Ah for the 911, Model: 911, Model Year: 1965-1973, Part number: 999 611 014 91, Availability: 01.03.2009". Pelican lists them at $189/ea and a special order.

An Interstate Battery U911 is also an exact fit.

There are other options such as Miata, Oddessy or Stinger batteries as well.

Also consider that unless you are a champion F1 driver, chances are you will not detect a handling difference between a single and dual battery setup.

[RDM]

Because I don't want a tub of sulfuric acid sloshing about inside my trunk, I go with an Absorbed Glass Mat (AGM) battery. The acid is absorbed into a fiberglass mat wound (in the case of an Optima) in between the battery plates. No liquid means no leaking, which means no acid-bathed bodywork.

One battery is enough to do what you need. You won't feel the difference.