jhbrennan

The correct size is the H7. While the W and H are the same on the H6, H7 and H8, the H6 is about 1.5 inches shorter than the H7 and the H8 is about 1.5 inches longer. Some use the H8 but the hold down clamp may have to be modified. The H7 is an exact fit and probably has a few more CCA. Take it back and get Way-Mart to install the H7.

"02996ttx50

^ fully agree. get an h7 or prepare to shortly.

with the unusually high parasitic drain these cars normally exhibit, the last thing you want to have as a fresh replacement is one with fewer CCA's than are factory recommended. 790. just because the lower cca battery starts the car, doesn't lend hope it will last even as long as the 790 cca h7's do. these cars are voltage hogs. simply put, the car starts one day, and won't the next.

also, if you don't have one yet? get a trickle charger. many of us use a 60$ ctek 3300.

Carlo_Carrera

The CCA number has nothing to do with the battery's ability to deal with parasitic loss.

I had a DieHard H6 in my 996TT and it lasted seven years, yes, seven years. The Walmart battery this fellow bought is fine.

"02996ttx50

i assumed, however mistakenly(?) that if the cca's were lower on the op's choice ( 730-h6 ) than the cca's of the battery porsche factory recommends for the car, ( which is actually the same as for a boxter! ) then the battery would be "weaker" out of the box and a dubious "long term" choice. but your experience suggests otherwise..but, why would anyone opt for a lower cca recommended battery than a 986 boxter uses?!

i would imagine though that lower cca's would at least suggest if not confirm that the lower cca battery had less out of the box "on demand juice" than one with 790 cca's?. so, how wouldn't that translate into less battery power? i can't imagine. but if you're saying that cca's have nothing at all to do with the intrinsic power of the battery, and that the "CCA" designation has no bearing on a batteries "strength", one over the other? then i have learned something and appreciate that. congratulations also, on possibly the longest lasting battery in a 996 turbo.

btw. nowhere did i attempt to correlate the inherent parasitic drain with the size of, or the cold cranking amps of, any battery in question. the car's intrinsic parasitic electrical "drain" - which no one could argue against - has to do with the CAR lol. not the battery.

still, less isn't "more".

Carlo_Carrera

Yes, the CCA has nothing to do with battery longevity or resistance to parasitic loss. The CCA number is just the amount of start power the battery can deliver at 0 degrees F. It is not a measure of the batteries all around strength.

Sometimes less can be overall stronger.

"02996ttx50

ok, but what have i posted that suggests i believe that the size ( or CCA ) of ANY battery, impacts the battery's "resistance to parasitic loss"? i haven't.

though i do now understand that the cca has NOTHING at all to do with the battery "strength" though i am not "fully" convinced lol

Carlo_Carrera

Your second sentence in post #17.

...with the unusually high parasitic drain these cars normally exhibit, the last thing you want to have as a fresh replacement is one with fewer CCA's than are factory recommended.

Not "strength", "all around strength". There is plenty of info on CCA via Google.

Also keep in mind Porsche likes to over build things. Other V6 cars out there work just fine with batteries with CCA numbers in the six hundred range.

"02996ttx50

i see what you mean now. i misspoke.

but they sure didn't "overbuild" the accumulator lol.

in any event, i'm gonna stay with a 790 cca battery, notwithstanding your anecdotal experience with that h6.. 7 years, huh? legendary

Kevinmacd

A cell can short out unexpectingly. Lot of times during the initial start they go. What happened is a cell went bad and the battery could not deliver the current! I bet your charing cables got pretty warm, a true sign of a shorted cell!

wross996tt

All good points. My experience suggests every Porsche I have owned is hard on batteries and require the batteries to be at optimal levels to start the car (even though other accessories still work). Battery technology still has a long way to go...If the battery goes below a certain charge level, it is damaged forever and can't be "re-charged" to new. This can happen at the cell level. The suggestion for trickle charge is spot on. I opted for the Interstate MTP93 which has 850 CCA.

"02996ttx50

this mirrors what happened to me a month or so ago. i had not been driving the car regularly, only trickle charging sporadically, and lo and behold, after a quick jaunt down the road, it wouldn't start up again. no warning at all.

this on a barely two year old interstate. once it's dead, i wouldn't have any faith at all it will ever be as good as it once was and that's the last time i conduct that experiement. dead battery gets an immediate call to AAA. but i DID just get a new ctek, just in case it too was failing lol

Kevinmacd

I have never had good life with Interstate batteries in my previous Porsches! In fact, about a year ago I changed out an Interstate that was about 2 years old, and bought an oversized Bosch! So far so good.

T10Chris

If dont drive the car a couple of times per week definitely need a trickle charger or pull the negative cable on the battery.. leave your front lid cracked if you pull the cable, but if does get closed you can connect to the fusebox in the driver's footwell to give it power to open, or can relocate the manual release to an easier to access area.

I didn't charge mine and the car sit for 3 weeks so it didn't start when I went to move it- checked battery voltage and is 7.4 so pretty sure it won't ever be right again so plan to replace it. Bosch battery, OEM spec, 1 year old. These cars have a constant drain.. I've monitored it with multimeter connected and checking it frequently over the course of a few days.

mfanatic325

I will definitely be getting a trickle-charger, regardless.

But in any case, I just went with whatever battery was suggested via the Walmart site. If they're for whatever reason wrong, well, at least I have their 3+2-year warranty
In fact, if this battery DOES fail prematurely, I could potentially be getting more "bang" for my buck since Walmart's merchandise return policy is pretty good

T10Chris

Yep, can't really beat the warranty they have in case of another failure.

I'm thinking of going another route, lightweight battery maybe even Lithium-Iron.. 5.5 lbs and allegedly cranks better than the typical lightweight Odyssey, etc; plus it is lighter. Seems like a win/win. Haven't made up my mind yet. Your idea is solid and may copy that as well to avoid hassles