peterp

Similar story. When I bought my 996.1, the Interstate battery that was in it was 5 years old -- it was working fine but I was just going to replace it proactively. I actually placed an order online for a battery back then, but it didn't go through for some reason, so I just never got back to it. The Interstate (non-AGM) lasted 6 more years (total of 11). Replaced it with an Interstate non-AGM H6 from Costco.

I think the H6 is a few pounds lighter than the H7, so I now have a 2800lb 996! (2901 lbs - 4 lbs = 2897lbs).

Interstate is just a very safe bet, and if you're a Costco member, it's very inexpensive. I didn't care about cost for the battery replacement, I only cared about quality, but Interstate also happened to be inexpensive.

allcool

Not sure where you got your AGM info but its not accurate imho...

I've used AGM for decades now in RV's, boats, cars, bikes, jetski, sleds, etc... Very familiar with them, especially Odyssey, but now have a H6 Walmart AGM in one of my 996.1 cars. On sale for $128 a few months ago with a 4 year non pro rated replacement warranty.
It works very well. No more slowish hot crank. Full charge gets it higher than any other AGM I've ever had at 12.82volts. Johnson Controls makes it, and others likeDuralast®, Diehard®, Kirkland®, Motorcraft®, and Interstate. JFYI,Brookfield Business Partners bought out Johnson Controls a few years ago...

1)" non-AGM are more tolerant of discharge events"

Not sure what you mean by discharge events..? But regardless, if you mean deep discharge,,, AGM are very tolerant of deep discharge. And their long life span and warranty show this...

2) "it's sometimes idle for a week or two, so I prefer non-AGM"

Thats where AGM really stands out from wet cell lead acid batteries. A good AGM can sit for a year and only drop a few 1/10's of a volt. They hold charge amazing well, much much better than wet cells, not even a question of this....

3) " non-AGM version is 6-7 lbs lighter than AGM"

For the same weight, its not unusual that an AGM battery offers 1/3+ more power than a lead-acid battery

And with no requirement to vent the agm, no acid spills is a great benefit imo.
Yes some agm batteries do have vent tubes or more accurately pressure relief valves that very very rarely will need to vent in an unusual circumstances like a total direct full short permanently left shorted out. I've never seen or heard of an agm venting, but if you do get a agm with a vent tube by all means connect it if ya want. But my guess is it will never be used.
In comparisons, a wet cell constantly 'breaths' thru its vent tube.

jmo

DBJoe996

^^ is all correct and accurate.

996C438

Two weeks ago I witnessed a AGM battery spewing acid mist out of the vents . The passenger side was vented with the OEM tube . The battery for whatever reason built up so much pressure that it blew out the drivers side vent cover . It literally had a mist stream shooting out over 3 ' away .

Granted this is not a normal occurrence but it can and does happen . If I hadn't seen it with my own eye's I would not have believed it . So yes an AGM battery can make a mess just not as easily as a conventional wet cell battery .

peterp

First of all -- I literally said "I don't think you can go wrong with either Interstate AGM or non-AGM", so I wasn't disparaging AGM, just explaining my reasons for going non-AGM.

Second, my non-AGM Intestate lasted 11 years in the 996, which has parasitic drain like most modern cars. A 4-year warranty on the Walmart battery doesn't impress given the 11 years, but I agree non-prorated is pretty cool and unusual. In my vintage car, with no parasitic drain, I just replaced the non-AGM battery that was 15 years old, proactively, -- it was still working fine, I just wanted the piece of mind of replacing it because it was FIFTEEN years old. I never use a tender on either car (I do slow charge it if either has been sitting a really long time, but other than that I don't touch the battery). I think I'm pretty happy with non-AGM at 11 and 15 years. I suspect other people would be too. Both cars crank fine always so I don't need the extra power of AGM. I stated very clearly AGM perform better in my post -- though I think you have severely overstated it at 33% better. Weight wise, the Interstate non-AGM H6 (the model we are talking about for the 996) weighs 38.9 lbs versus 45.4 lbs for the AGM, so it's 6.5 lbs lighter. The amp hours for the AGM and non-AGM are identical at 70. The CCA for AGM is 760 vs 730 non-AGM -- a 4% difference. Cranking amps is 950 vs 910 -- also a 4% difference. That's an "apples to apples" comparison of the same brand and same size battery. I think I'm going to be able to live with the 4% difference of the non-AGM (especially since I just did for 11 years with the prior battery).

I've had 3 Optima batteries, 2 red top and 1 yellow top an they all sucked. They worked great for a while, but a after running low from normal parasitic drain while sitting for a long time, they died. I've run the non-AGM low a several times over the years from sitting parasitically too long and it lasted 11 years. When I was proactively replacing my 15 (fifteen) year old non-AGM battery, I wanted to buy one of those vintage 60's batteries (that look like tar-top but are modern batteries inside). They only have them in AGM. When I talked to the seller, he was adamant that you need to run a AGM-compliant trickle charger for a full day at least once a month, even if it isn't low, because the charger has a cycle to repair the cells. I don't want to use a tender and have never needed to use one and I got very long life out of non-AGM. I've also heard from others that AGM's aren't as tolerant to discharge (there are also posts on RL saying same if you read other battery threads). Which battery is best depends how you use it (how long do your cars sit idle?, are they parasitic?, do you use a tender?)

For my Macan, which will benefit from the AGM performance advantage with automatic engine start/stop, and which has a charging system designed to work with AGM, I will absolutely use an AGM battery when I need to replace it.

Everyone can pick what they want to use for their needs. I gave a balanced overview. AGM performs better. AGM weighs more. Non-AGM have proven to be very durable (11 and 15+ years) in my "worst case" scenario of having cars sit idle for long periods of time without ever using a tender. I think my post was pretty damn good, and accurate, and fair.



Apples to Apples Interstate H6 non-AGM vs AGM specs:

SSDVC

So I make some lengthy trips overseas and my C4 sits for months at a time. This last trip (2.5 months) was the last straw for my current battery, which is a AAA group 94r battery. Don't know the age, or how long it's been in there, but it has got to be at least 5-7 years old, maybe longer.

Anyway, I am wondering, since the car sits for longer periods of time, if I should go with an AGM battery or stick with a wet cell? Here is what is in storck by me:

Walmart has an AC Delco 94r AGM on sale for $195 or an EverStart H7 AGM for $180.
AutoZone has the Duralast platinum AGM for $250, Advanced Auto has the DieHard H6 Platinum AGM for $255.

I guess the other question is, should I stick with the 94R/H7 or the smaller 48r/H6 Group size, as all the web sites recommend? What would be better for my convertible?

Thanks

Truth be told, I am tempted to get the Walmart Everstart for $180 and call it a day. Thoughts?

Mike Murphy

I went with a smaller, lighter battery for $130, Costco, Interstate. My 99 cab doesn’t really have anything crazy for power draw except heated seats. I’ve had this battery since 2017 and it’s been great. I’ve never used a maintainer, as I always drive my car at least every 3 weeks. I also bought one of those lithium jump-start packs and I leave it in the car just in case.

996C438

I am currently running Walmart Everstart wet cell batteries in my Boxster and 996 C4 . Let's face it Walmart doesn't make the battery there are only a handful of manufacturers in the world . I do use maintainers on both .

If you have an issue there is a Walmart close by . Their price is very competitive and the warranty is solid . I believe a maintainer is key to making batteries last regardless of wet cell or AGM .

pdxmotorhead

The bulk of the auto products Walmart sells are built/packaged to their spec. Often a lower level than the standard item.

Numerous friends have been burned by their tires for instance. Both times I checked ,
their BF Goodrich All terrains had 1 less ply rating than the standard offering.
Their Mobile one oil is also packaged to their spec. It often is missing some of the test ratings.
The printing on the bottles is just slightly different. One day when I'm bored I'm going to buy a
bottle and send it in for testing with a bottle from a regular auto parts store..
Their Die-Hard batteries are about 1.5 lbs lighter than the ones at the dealer..

Gary12000

I was forced to consider my options and went with a Trickle charger, one weekend I forgot to lock my 996 fully, and after non use for three weeks, it was totally dead battery, the battery is an interstate and less than a year old, prior to this the car was used every one to two weeks and started fine every time.

It is my understanding from reading here that the 996 doesn't go to sleep fully unless you lock it with the remote or perhaps even with the key in the door.
i expected to have to go down the path of which battery to buy next, however as i am a believer in trickle charging if the tender is smart enough to maintain rather than charge all the time..., i decided to research and then purchase a Ctek trickle charger, it just gives me piece of mind... it was expensive at $140 bucks, but it has several modes for wet cell or AGM and can do motorcycles as well so it can little batteries..

so if like me you are having start anxiety consider a Ctek, which i read is the Porsche brand of choice albeit re-badged.

allcool

Well, my understanding is when alarm is activated and in full protection mode, a small battery drain is constantly happening. In a matter of weeks battery will be dead.
With car not locked and alarm not activated, all doors, lids, trunks, etc, closed, the least amount of battery drain occurs...

jmo

Mike Murphy

I have found no difference on my 99 Cab locked or unlocked after 2-3 weeks of sitting. It just starts up. I haven’t measured drain, though, so it’s all anecdotal and a data point of 1.

Gary12000

Gotcha well same sample size of one, mine didn't go dead until i left it unlocked, i don't have an aftermarket alarm fitted, but who knows what parasitic drain i have if any, i have disconnected the frunk light as i found mine has been fitted with a little LED gizmo with its own electronics, and a heat sink that gets burning hot when its on for longer then a few minutes.. i was suspicious of that and as i don't think the frunk light is that important i just unplugged it.

allcool

Me also, anecdotal. Although I have read voltage of battery while connected to car, without alarm on, doors unlocked, and with alarm on in full protection mode. Can tell you on both my 996.1 & 996.2 the voltage drops slightly from day to day with alarm on. Without alarm on voltage still drops but not nearly as fast. I'll go from 12.8v on agm Walmart battery to 12.5 in a week or 2. Without alarm on might go down 1/10 of a volt in same time frame.

Ya, I know a amperage reading would positively tell the whole story. Might do that in the future when my bucket list of 996 jobs is done... For now, I leave both my 996 in garage top down unlocked alarm off. Can go for many weeks like this and still start right up. Not so if left locked with alarm on with a less than perfect older battery.

Speaking of batteries, my new Walmart AGM (5 months old) seems to be the best AGM I've ever bought. It charges to 12.8v routinely. Never had an AGM that did that. It spins over the 3.4 with authority and sounds like the most starting rpm I've ever had in this car with any battery....And holds charge extremely well for prolonged periods. Whereas every other AGM I've had over the years(dozens, had many Odyssey agm batteries) only charges to 12.6-12.7, and that is considered a full charge for an AGM.

pdxmotorhead

I put the battery out of my jeep in temporarily while troubleshooting a problem, its a 1260 CCA agm man does that thing spin over, too bad the hood wont close.. LOL