Dual Battery Options

[justacoupe]

In a Pelican posting, a Rayovac battery was mentioned as one option for dual battery cars (sold at Batteries Plus). That battery has been replaced at Batteries Plus by a model branded as a Duracell. It is the same battery (model number SLI70). Mine cost $71.99 each (after credit of $9 for each core). Including two pairs of charging posts and sales tax it was just over $170 out the door for the pair.


The side tabs need to be trimmed off (utility knife works). I also had to trim a bit off the bottom edges on each side due to battery box's radius'd edges on the bottom.













Here's how it looks installed on the passenger side in our '73E (original owners... 66,000 miles). I'll be adding protective covers to the positive side terminals:




Compare that $170 total to what Stoddard wants for their "original style" dual batteries (their part number 999-611-036-20). Those run $ 169.86 each but no sales tax = $339.72. Add estimated shipping of $25 and battery acid (shipped dry) at $16.00 for a total of about $381. Link: http://www.stoddard.com/999-611-036-20.html

Or, the Sonnenschein option: http://www.batterysales.com/downloads/A512-40.0-G6.pdf Their model number is DF75, and the cost is $195.95 each plus shipping so about $425. Plus, terminals or cable connectors need to be converted so maybe a total of $440.

Regards,

Bill
Grand Rapids, MI

[super9064]

Nice option, I like that the posts are on the side. Thanks for posting.

[Mocker]

Just to update and reinforce what Bill wrote: The model number for this battery is SLI-70 ("I", not the number "1"). My local Batteries Plus had it in stock. My plan is to go with the single battery, keeping it on a tender.

The other thing to reiterate is that it's a very tight fit! Very! I spent a few hours first with a file, and finally settled on a Dremel, to remove the bottom platform off both ends of the battery in order to clear the radiused (not square) corners of the box. Still took some hammering and persuading on the corners of the box itself. Once in, it looks like it really belongs!

[mohrgan]

Another option is this AGM battery for a Mazda Miata. I have two of these in my car and they need to be spaced out a couple of inches with a piece of 2 x 6. These are AGM batteries so the likelihood of them leaking is very small.

http://www.batterymart.com/p-12v-maz...a-battery.html

[speedo]

Great timing as I was just about to post the same question, although I am deleting the passenger side battery. Are the Duracell and AGM powerful enough to only use one battery? Are there any optimus or oddessy alternatives? I am +++ on the front facing terminals.

Speedo

[304065]

I used to use a Hawker PC680. You delete the starboard battery by removing the cable from the port clamp.

It doesn't look like it but it would start my 2,2 race car from stone cold in the mornings at the track. The power density is amazing. The aviation approved version (3x the price) would happily swing the 74" prop on my Citabria under the same conditions.

Once you deviate from concours, might as well go with a nice light solution. It doesn't help the polar moment of inertia however. . . .

[Flieger]

Actually it does help the moments of inertia, much more than it degrades the weight distribution. Moment of inertia is mass times radius squared, but weight distribution is just weight times radius. As the better compromise you would want a heavier battery in the smuggler's box.

[304065]

Actually it does help the moments of inertia, much more than it degrades the weight distribution. Moment of inertia is mass times radius squared, but weight distribution is just weight times radius. As the better compromise you would want a heavier battery in the smuggler's box.

Max, I agree, but the definition of "help" is inverted. For a street car you WANT those heavy bricks up front.

the "polar" part is wrong it's not the polar moment, just the moment

[Flieger]

No, you want a lesser moment of inertia. It makes the car more stable, as would lengthening the wheelbase and holding the inertia constant (even if keeping the front/rear weight distribution the same). You can think of it as the tires having more effective leverage if the moment of inertia is less.

edit: My definition of stability is tendancy to return to a trim state. Meaning that if you change the trim (steering wheel angle) the car should respond very quickly and if you keep the wheel pointed straight then it should want to keep going straight. Lots of yaw damping and high yaw stiffness.

[merbesfield]

Lots has been written and discussed about batteries. There are no perfect options IMO. That being said, there is no way I would ever consider putting an old fashioned lead acid batter in my early Porsches. I have done a couple of pan replacements and have no desire to do them again. The Tin Worm is bad enough on it own, I'm not helping it. So that leaves us with a single AGM battery that fits. You can do the research, but basically, they all appear to be made by East Penn and are rebranded by numerous companies. Here is a link to a thread on the Bird giving more details. There are differences in lead locations between SWB vs the LWB. What I have done is place the battery on its side on the passenger side of my LWB, this is the beauty of the sealed AGM battery. I always hook up to a trickle charger and have not had any issues with it not starting on the first attempt. These batteries do not have the same power as the larger lead acid batteries, but again, I have not had any issues. I have not figured out my final setup for the SWB, but the terminals are in the correct locations and it will easily fit the location. If you do kill an AGM battery, they do require a different method of charging, which I will not get into here. I am by no means a battery expert, just what I have had to learn to figure all this out for my old cars. It is way more than I really cared to know about batteries. I figured maybe I could save some folks a little time.

The general part no. is 8AMU1R. If you do a search for this you will see many choices for several vendors reselling what appears to be the same or very similar battery. So I would shop on price and convenience.

Sold as Deka, Marathon, Dura Last from AutoZone and so on. Here is a Marathon from Amazon for $80 +$16 delivery.

http://www.amazon.com/BatteryMart-co...m_cr_pr_sims_t

http://forums.pelicanparts.com/porsc...t-battery.html