What do you use to maintain power while changing the battery in a 996??

I'm going to get a new Interstate MTP-48/H6 to replace my 11 (eleven ) year old Interstate MTP H7 battery that finally failed. What are most people using to maintain battery power while changing the battery? I think I have one of those 9v maintainers that plug into the cigarette lighters, but I don't know if it works or is a good idea to use on a 996 at 9 volts (also wondering if I need to leave the key on for it to work). The other option I have in mind is to use a battery tender clamped directly to the battery terminals, but want to make sure voltage stays regulated around 12ish volts when the battery is no longer connected.

All I can think about from your post is you had a battery last 11 years. Holy ****!!!

It's not going to hurt the car to disconnect the battery for a couple minutes.

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My understanding is that radio codes, power window alignment and other things get reset as soon you disconnect power in the 996. I haven't been through it, so I don't know if that's a big deal or not. Yeah, when I got this 996 it was already 6 years old and I was going to proactively replace it, but then I just decided to see how long it would go, and now I know . Interstate batteries are the best in my opinion. Most battery brands are built in the same factory (Johnson Controls), but each brand has their own designs and specs, and Interstate seems to be the best from a wide variety of mechanics (that has been my experience also). .

The power window alignment is easy peasy. Roll the window all the way down and keep the button pressed down for 5 seconds after the window fully retracts, then roll the window back up and keep the button pressed for 5 seconds after it rolls back up. Do this once on each window. The stereo code thing is only true for Mk1 stereos, the Mk2 ones do not need a reset code after a new battery. Biggest radio PIA I've had after a new battery is I had to pull the radio fuse because the radio kept turning on/off on its own. This does not answer your question about powering the car but it kinda answers your question about how big a pain it is to reset everything. If you don't have your radio code available and you have a Mk1 I can understand your concern.

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So I'm looking at at least 10 seconds, per window!! The radio won't be a problem. I think I remember that some of the engine management remaps itself after a reset -- not at all positive about that. That has me wondering if a reset might actually be a good thing to do. I certainly don't care about the radio and window alignment (now that I know how simple it is). Redoing the window alignment also might be a good thing after all these years.

I used this when I swapped my battery this past summer: Amazon Amazon

My car stays on the battery tender jr year round, anytime it’s not driven for more than a week. Great success over a decade using their products. Amazon Amazon

I�ve had to cut power to my 99 Cab many times. I�ve never had to re-program or adjust anything besides the radio. Some of the power cuts were for weeks and I still didn�t have to recalibrate anything, top included.

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I havent had to reset anything in my coup either with the mk1 or 2 electrontics that r in there now. The only thing that might be an issus is if u r in CA and need to trip the emmisions readiness monitors for an inspection.

I�ve disconnected the battery in my 2004 996.2 lots of times and only have had to reset the windows (and only sometimes at that). Disconnecting the power DOES reset all of the ODB-II readiness monitors, though. And one of them (forget which one) takes forever to reset (weeks or months). So if you have a smog check coming up, I�d do it before you disconnect the battery.

Just swapped the battery this weekend, no issues. I only had to reset the windows because they went out of alignment when trying to start on a dead/weak battery and they freaked out a bit.

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Thanks for all the great feedback. I'm inclined to just disconnect, and part of me thinks that might actually be a positive for the engine to remap itself. I won't have to get inspection for a while -- just trying to figure out if it's better, neutral, or worse to reset engine management (guessing either neutral or a positive rather than a negative).

I was going to stick my CTEK in the cigarette lighter but haven't tried it yet. My interstate is 6 years old. Maybe it'll make it another 5 like yours. I don't want to deal with the pain of the OBD readiness. If you try the cigarette lighter let us know what happens.

Another vote for doing nothing. I had my battery disconnected for a week when I was doing the heater foam thing. Reset the radio, reset the windows, done. I didn't feel any difference at all relating to engine mapping. That's not to say it didn't change, just that it did not negatively affect the way the car starts and runs.

Your car, your decision. FWIW as a professional I always used one of the little 9v cigarette lighter power sources to keep alive all memories. Biggest customer complaint is "radio station pre-sets".. Things that MAY be effected by loss of memory; radio station pre-sets radio code seat position memory rear view memory dip memory climate control memory Trip-meter & OBC memory sun roof memory window memory transmission shift memory (Tip) engine control memory While clearing memories and re-setting can fix some issues, if you have the power source it makes since to use it... (If you are not having any issues)..

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Thanks for chiming in --- great feedback. I guess I'll use the 9-volt cigarette thing (assuming I can find it, I bought it 6 years ago when I was first thinking of proactively changing the battery ). A couple of questions about the 9v cigarette plug: 1. Does the key need to be turned on for the cigarette lighter to power the car; 2. Does the 9v battery last a long time (say an hour or so to clean everything before reinstalling the new battery), or do I need to work quickly before the battery drains?

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ON a 996 the Cig lighter stay hot with key off. If the 9v is fairly new,no worries it will last a long time. The power drain after key off is only 35ma...

Thanks for all the great advice. I changed the battery last night. I used the 9v cigarette lighter plug, had the battery out for an hour as I cleaned up everything then put in the new battery. Interstate has always been my favorite battery, and with 11 years on the last Interstate, I went with Interstate again. I bought it at Costco -- Interstate H6(48) model for $115 -- 730 CCA. The 996 battery tray is built to support three sizes, H6 (10-ish inches wide), H7 (12 inches wide), H8 (I'm guessing around 13.5" wide). The old Interstate was an H7, I couldn't find which one would be used for the 996 (all the Interstate guides point to the H6) and the H6 was in stock inexpensively at Costco so I went with that. When I looked up the weight difference, it was about 10 lbs H6 vs H7, but when I pulled out the H7, it felt a lot heavier than the H6, so I'm guessing the weight savings are probably 10-15 lbs with the H6, so I'm glad I went with that. I intentionally went with the Intestate wet cell battery versus the AGM Interstate. The AGM's do perform slightly better, but I think they are a bit fussier about how they are recharged and don't handle being run down as well (with can happen when cars sit if you don't have a trickle charger connected). AGM/s perform better, but I feel wet cells are still more durable in adverse conditions.

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I'm looking at an Interstate battery and also the Costco route. When looking at Interstate's site I get a few options for my 2003 Targa, but don't know which to pick: https://www.interstatebatteries.com/...sche-911-h636l Costco only shows one: https://costco.interstatebatteries.c...747&Country=US My indy actually recommended an H8 for better starting and overall performance. He said in their shop 996 things improved with that versus the H7. I was hot on AGM, but after your comment maybe that's not the route to go. My car only gets driven now a couple times a month. Otherwise it sits on the tender, but if I forget, I would need something that won't ruin it if it gets run down.

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Interesting -- the spec for your 996.2 seems to favor the H7, while the spec for my 996.1 favored the H6 (e.g. Costco only shows H7 to you and only H6 to me). I think Costco will only sell you what is specified for your car, so you'd probably have to tell them you have a 2000 to get the H6. It may be that the 996.2 has more parasitic drain when sitting, hence the H7 spec. I guess I would go with H7 in your case given the 992.2 spec and that your car sits a lot (as does our 996.1). It looks like the weight advantage of the H6 is only 7.1 lbs ( https://www.interstatebatteries.com/...911-h636l&c=US ). I think Interstate's green top batteries are better quality, so I would go with the green H7. Costco's model number is slightly different than the Interstate battery's model number, but I think they are the same. Others may have a different opinion on AGM's than mine, but I think traditional we cells are just the safest bet. I had red top and yellow top Optima batteries in the past (on different cars, not a 996), and I wasn't impressed with either one.

Swapped out my 14+ year old battery in November. Just disconnected it and dropped the new one in; didn't lose any settings for seats, mirrors, radio. Don't over think it; changing the battery on a Porsche is no different than on any other car ...no need to maintain power while doing it. FYI: I give credit to the CTEK battery maintainer for keeping the last battery healthy for so many years!

I did the exact same thing as you - with the Costco battery and size and all that. That was 5 years ago. My 99 doesn�t really need the high powered battery the car could accommodate, despite having heated seats. The huge capacity batteries are really good for idling cars that have a lot of accessories (lights, heaters, outlets, etc.) found mostly on premium SUVs. I try to never idle my car, and I don�t run lights or the stereo without the car running.

Wow, 14 years, that�s amazing.

What is somewhat odd on the Interstate batteries is that there are vent holes on both sides of the battery. I plugged the 996 vent tube into the passenger side of the battery (same as it was with the prior Interstate), but the driver-side vent hole on the Interstate is also open, to I'm not really sure what the point of the vent tube is (since it only connects to half of the vent holes on the Interstate). .

I think one of those should be plugged on the battery, and the battery should have come with a plug?

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You would think that it would come with a plug, but it doesn't, which is pretty disappointing. I decided to look for 996 battery replacement videos to see if somebody addressed the venting plugs, and found the video below from Heidi and Frannie's Garage. Their videos are always the best -- they cover everything in detail and I always learn several things from them, even for things I think I know well, or that is essentially brainless (like replacing a battery). The battery tester they use at the beginning is pretty cool, but probably unnecessary. The things I hadn't thought about that they covered is that: 1) if you use an OBD2 port to retain the car settings, that the positive terminal will be hot (12v) when disconnected from the battery, so wrap the terminal in a latex glove; 2) Batteries often don't come with plugs, so take the plug from the battery that was previously installed; 3) Those plastic covers that cover the terminals when you buy the battery can actually be snapped back in after you install the battery. I think they should have mentioned the 9v cigarette plug option also (unusual for them to miss anything), but still a helpful video. Anyway, back to my battery. Unfortunately my old interstate didn't have a plug on the opposite side either. Nothing leaked out because the battery tray was pristine, but not ideal. I happened to have a variety size box of vacuum tube sealer caps and found that the blue ones fit snugly into the vent hole on the driver's side of the new Interstate, so now it is sealed. You Tube

Do you guys think this old charge-o-mat plugged into the cigarette lighter will work for the swap?

I have one of those on my 996.1, plugged in as the car sits for a week or 2 a time . I bought my 996 with a new battery installed in January and as this came with the car I threw it on. So far so good!

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I would think this would work. I used the 9v battery via the cigarette lighter and it worked fine. When powering it through the cigarette lighter, you can't really tell that it's doing anything (e.g. the front trunk light doesn't come on when have it open), but it's apparently keeping the memory alive because didn't have to reset anything after. The plug-in unit should be fine I would imagine as it is 12v (versus 9 in my case). Those plug-in trickle chargers are normally design to be used with a battery in place, but they presumably regulate voltage to a reasonable limit when the battery isn't there.