New Battery for the 944

[yundar]

Hey Guys... Just wondering what battery you are using in the 944? I have an 87 and I need to get a new battery. I wanted to get a sealed AGM type but no one seems to make one for the 944. I tried looking for one from a different model that would fit but they are all too tall. I ended up getting a standard replacement one at the local tire dealer (Les Schwab) but it is a non sealed type and requires a vent tube. I understand this is stock but I don't really like having to go back to a vent tube battery. I checked a few other places and Napa was the only other place that had a battery and it was identical to the new one I bought save for the stickers. It was listed as a group T6. The battery that came out of the car was a group 40 or 41 but no one is selling that size that I can find. The car is used for autocross and I would like to get it out on the track this summer.

Thanks, Andy.

[wildcat077]

Andy,

The Interstate MT40R is a good fit for a 944,we have Interstate batteries in pretty much all
our vehicles and they're a good value !

Cheers
Phil

[Rasta Monsta]

+1 on the Interstate. Costs a bit more, but 100% worth it.

[sausagehacker]

I have this one in mine, it's great and the battery hold-down is a direct fit to the flange.

Super Start Premium 40R72 - Battery | O'Reilly Auto Parts

[AaronM]

While a group 40R battery will fit, it's not the right battery for the car.

Interstate's website lists the MTP-91 as the correct battery for the 944. The MTP-91/T6 is a 700 CCA battery, compared to the smaller MT-40R's 590 CCA. Interstate's own site does not list the MT-40R as appropriate for any Porsche.

I'd recommend sticking with the more powerful (and correct for the car) group 91 batteries if at all possible. I've heard that the slightly larger Group 48 batteries may also work (and allow you to find an AGM battery since the only group 91 batteries out there are traditional wet cells), but I have not tested that myself.

[sausagehacker]

Oh wow, thanks for the info, I had no idea. Next battery will be the one you suggested... they only last 2-4 years here in TX anyway!

[wildcat077]

For the record,my 944 is a race car and the MT40 is not as tall as the MTP91,which works out well for my needs.

Cheers
Phil

[AaronM]

Originally Posted by wildcat077

For the record,my 944 is a race car and the MT40 is not as tall as the MTP91,

Both the MT-40R and the MTP-91 are spec-ed by Interstate at exactly the same 6.88-inch height. The difference is that the MTP-91 is a bit less than 1/2 inch longer. Width and height are identical between the two.

It's the Group 48 batteries that are taller.

[thomasryan]

See what Sonnenschein has to offer.

[ckelly78z]

I would think in a race car you would want the smallest/lightest weight battery that would still start your car and operate your fuel injection/gauges. You could also run underdrive pulleys for lack of power requiring options which would free up a few HP.

[CHICKS]

Interstate is a good battery, just did one in my Porsche, and another in my Subaru.

[DannoXYZ]

I use a LiFePO4 battery and save about 40-lbs.

Previously, I used Group-35 battery from Costco. That one is about 5lbs lighter and lasted 12-years. I just had to extend the short ground-wire to the body about 3" to fit (the terminals are reversed).

[GTR34]

I've been using an optima red top Seems to work great for me!

[Rasta Monsta]

Just for laughs:

[DannoXYZ]

That's cool! Back when I had a Supra, I used a motorcycle battery for a while. Some of the Honda Civic and Toyota MR2 batteries are about that size.

[yundar]

Cool guys! Thanks for all the good ideas. I should be able to come up with something this weekend.

It looks like the Interstate MTP-91/T6 that Chicks is showing and the O'Reilly Super Start Premium 40R72 that sausagehacker linked are the same thing. They have the individual vent caps for each cell on the top and need to be externally vented. They even have the same "Made in Germany" sticker on the top which I suppose is a good thing. I wouldn't doubt that they are even made in the same factory. These are also identical to the Les Schwab one that I bought.

Aaron... Seems like the Interstate MT40R types (that Wildcat posted) were an older style for the 944 as that is what was in my car. The dealer told me they are not being used any more and have gone to the T6 style that you recommend. The only thing I didn't like about those were the external vent tube. It's funny that this is being called the new type when it is probably closer to what a 944 would have originally had.

Anyways... Thanks again for all the info. Andy.

[AaronM]

Originally Posted by yundar

It looks like the Interstate MTP-91/T6 that Chicks is showing and the O'Reilly Super Start Premium 40R72 that sausagehacker linked are the same thing.

No, they are not the same thing. "40R" and "91" are group codes. They denote specific dimensions for battery size and the type of hold downs used. The Group 91, while the same height and width as a group 40R, is longer, by about a half-inch and has hold downs all around instead of just on the long sides.

Originally Posted by yundar

Aaron... Seems like the Interstate MT40R types (that Wildcat posted) were an older style for the 944 as that is what was in my car. The dealer told me they are not being used any more and have gone to the T6 style that you recommend.

The dealer is a bit mistaken.

The Group 91 size is not "newer." It can be, however, harder to find in the US than the Group 40R size, which is used in many, many Ford and Mazda products. Because it is the same width and height as a Group 91 battery, the Group 40R will physically fit in the 944's engine bay and will secure with the same hold-down (since the hold-down is dependent on the battery being the right width, not the right length).

If we want to get very technical, the 944 specifies a "T6" battery, which is a DIN size specification. The DIN "T6" does not exactly correlate to a US "Group" size, and both the Group 40R and Group 91 are close enough to be physical fits. The problem is that, with less than 600 CCA, the Group 40R batteries are, in my opinion, underpowered for the car if you plan to use it in even slightly cold weather.

With the already problematic grounds on most of these cars, I think it's best to have the more powerful Group 91 batteries (700 CCA) unless you're running a racecar and only need the bare minimum.

[DannoXYZ]

Here's the battery I used. Amazon - YTZ14S Z14S Lithium Ion Sealed Battery


Used it originally on my CBR600RR, which saved me 10-lbs off the bike. Then went to an even smaller size to save 11-lbs. Figured, what the heck, toss it in the 951 to save +40lbs and see what happens. I measured the typical starter-current draw and it's usually 90-95 amps for 2-seconds. This battery puts out 290-CCA and doesn't drop with lower-temps like lead-acid batteries. At -20F, it still puts out 290-CCA while lead-acid batteries will have dropped to 1/2 their rating. Been working great for the past 2.5-years.

Did I mention it saves +40lbs from the car? And in a bad high-up location too.

[AaronM]

Originally Posted by DannoXYZ

This battery puts out 290-CCA and doesn't drop with lower-temps like lead-acid batteries. At -20F, it still puts out 290-CCA while lead-acid batteries will have dropped to 1/2 their rating. Been working great for the past 2.5-years.

That's just plain false. Lithium batteries lose performance as they get colder just like any other battery. They lose less performance than traditional lead acid/AGM/Gell batteries in the cold, but they absolutely do lose performance as temperature declines. There's a reason why the Lithium batteries in my camera lasted for only about 100 photos when I was in the Alaskan interior at -40F but lasted for more than 400 photos when I was shooting here in WA on a 70F summer day.

Lithium batteries are also very sensitive to charging strategy, so putting one on a traditional overnight bench charger can destroy it.

They're great for saving weight, but unless you're tracking the car, I just don't see a reason.

[Catamax944]

How about 3 lithium ion bike batteries in parallel.
Will it be enough for a daily driver 944 ? Asside from a significant weight reduction will they have a much longer lifespan ? For the money spent i would be looking for a min of 10year life out of them , would that be realistic ?