Battery.....size matters

[905084]

Anyone replace their battery lately? Had my A6 and RS go in the same week. Both show the same P/N (H8 size) but not true. RS is about 2 inches longer (or wider if you try to put it in the A6) . Anyone else come across this? I drilled and tapped the battery plate to accommodate the new battery. Ideas?

[JSRS6]

I came across the same when i got back from Afghanistan. it was the battery. i got a new one from advance auto, H8 size. Didn't worry about the rear clamp at the time, bolted the side clamp down really well. Oh, and i have a three year warranty on the battery, better than OEM! But i like your idea of simply drilling and tapping the plate, will do next chance i get.

[lswing]

Yep, Odyssey pcm925 and a 2.5 gallon w/m tank with pump fit perfectly in place of the old monster:) Luckily it rarely gets below 30 around here...

[hahnmgh63]

Been running the Odyssey 925t for about 3+ years now sucessfully. I do keep in on a Battery tender junior since I don't drive the car but once a week anymore. Just for more reserve capacity I'm thinking about going for the Odyssey 1200 next time, still 20lbs lighter than stock and I'll stick the 925t in the 911 or the tt.

[lswing]

hahn, thanks for chiming in with the good info. I still need to PP you some $ for the sps, thanks!

[kismetcapitan]

I wish I had had more experience with LiFePO4 batteries when I bought my two PC925s. They work so well on my bikes and have a surprisingly large amount of reserve capacity; I will eventually replace my PC925s with MUCH lighter 16-cell lithiums. A $600 investment ($300 a pop) but instead of 52lbs of battery weight, I'll have 10lbs.

[SteveKen]

I've wondered about this, too, as I've done musical chairs with the batteries from an A6 2.7T and the RS6 with my RS6. Even with less drag using the flywheel, etc. it still struggled imo. I would think that compression being the same would be the determining factor lower in CCA, but I'm also thinking that the battery being 10 feet of cable further from the starter might have a lot to do with it, too.

Plus the batteries I was using were pretty old (read originals).

I'm toying with the idea of a single PC925 placed in the engine compartment (shielded of course) in place of the SAI pump? That's about as close to the starter as you can get. I might have to try this when I get to the RS6 engine swap in the 6 speed S6. I know there's a good bit of room there.

BTW, I never feared getting stuck with a no-start condition with the 6 speed RS6. I always parked down hill when out and about and could always catch it in gear. lol.

[hahnmgh63]

I'm only finding a 20Ah version. Do you have a link to a larger LiFePO4 one as 20Ah would put it right between the Odyssey PC680 or 925 unless you use two and wire them in Parallel?

[Vdub]

The RS6 battery is in the back of the car, the A6 bat is in the box underneath the frontwindshield

[Tom Sawyer]

I'm starting to get some slow cranks with the weather dipping into the 30's here (TN)... We do get some temps below freezing here and there, do you think I'd be ok with with the 1200? I like the idea of dropping a little weight off the beast. The Lithium idea is intriguing too... as you mentioned a bit of an investment but nice weight savings.

Quick searching turned this guy up: http://www.ebay.com/itm/Super-B-7800-12-volt-Lithium-Ion-LiFePO4-Starting-Battery-UltraHigh-Performanc-/321006415147#vi-content

2.8 lbs...wow! Not sure if that's enough power but pretty amazing how light it is.

[hahnmgh63]

That LiFePO4 battery is only comparable in performance to the PC680 which is definitely not enough for our cars, two in parallel would be comparable maybe to the 925t that I'm currently using. Tom Sawyer, I have used my 925t down to the 20~30's but if it was sitting in those kind of temps for a few days then I would imagine it wouldn't have the reserve capacity to last. My garage gets no lower than the 30's and I do use a battery tender if the car is going to sit more than a couple of days. This is why I'm thinking about jumping up to the 1200 which has about 50% more reserve capacity than the 925t (which I have been using for 3 years), and is still lighter than stock by about 20lbs. And I do believe weight is weight but I think taking more out of the rear is less important than if we could take some out of the front.

[kismetcapitan]

I'd use two; I'm wired for parallel batteries in my trunk.

[Tom Sawyer]

I'd use two; I'm wired for parallel batteries in my trunk.

I really like your setup.... so clean without the battery hump. I may just go that route.... Need to do something fairly soon before I end up stuck somewhere with a dead battery!

[hahnmgh63]

Two of those 20Ah Lithiums would still only get you to about what one 925t would do, maybe slighlty more and for that kind of cost put it towards a set of Forged wheels and get rid of the OEM wheel anchors, stock wheels are very heavy.

[Dmb408]

Somewhat thread jacking here but would any of the Braille batteries work if price for mod was no object?...

[hahnmgh63]

Braille would work fine, they are similar in construction to the Odyssey batteries, and I think a little cheaper. If you do a search on the different forums it seems like the quality of Braille batteries varies a bit compared to Odyssey batteries.

[lswing]

The RS6 battery is in the back of the car, the A6 bat is in the box underneath the frontwindshield

Love the input, but we all know there's a battery in our damn trunk...