fc-racer

Hi there,

With the weather suddenly turning amazing here in the great white north, I wanted to take the condom off the car and go for a drive. I knew the battery would be low or dead because I forgot to disconnect the battery when I stored it two months ago.

Upon taking the cover off, the car wouldn't even disarm the alarm. Upon jump starting it, it still wouldn't hold a charge so I went searching for a new battery. The dealer wanted CAD$265 for a replacement battery. Given the relative poor performance of the factory battery, I went searching for a higher value battery.

Did a quick google and found Interstate batteries, made in the USA. Might as well support the economy down south, given that 75% of our exports go to you. The Interstate website says that a 2005 997 should use the MTP93. Fortunately, a quick search on rennlist said that we should be using the MTP91, however we'd have to use a different hole than the factory battery.

Upon replacing the battery, I found that the GT3 has a smaller battery than a regular 997 and the MTP91 is a direct replacement, no need to change holes or anything, it fits exactly like stock. Total cost for the MTP91 was CAD$165. To replace the battery, you need:

1. Interstate MTP91 battery with a vent kit (mine came with one for the Merkur XR4ti, which fit perfectly)
2. 10mm and 14mm socket
3. Undo the finger twist tabs on the battery cover
4. Remove the battery hold down clamp (on the passenger side) using the 14mm socket
5. Loosen the 10mm nuts on the battery terminal
6. Remove the negative terminal
7. Remove the positive terminal
8. Remove the vent tube (it pulls right out after some mild resistance)
9. I'm really light so I stood in the trunk, but the battery needs to be tilted back and to the driver's side to get it out of the tray
10. Reverse the above to install
11. Check the tightness of the clamp after driving it for a bit

Hope this saves someone the hassle of researching the correct size. Just a reminder that the Interstate website gives an incorrect battery size recommendation for the 997, you need the MTP91.

Cheers!

jcnesq

Thanks. I just replaced my 997S battery with the Interstate 2 weeks ago and went in asking for the MTP91, but they said the correct one for my car (which was exactly the same size as the original OEM battery) was the MTP-H7. I think the battery was $159, plus sales tax, and they charged me $5 to have a lawyer install it (now that's scary, huh?!). (The owner's son just passed the bar exam and is looking for a job, meanwhile helping out at the family business.)

todinlaw

Thank you, i will put that in my notebook, I am sure these batteries wont last more than a few years.

MikeBat

Hey... I resent that! I am over 200lbs, and I stood in the front trunk too!

Snowboarder54

Thanks, I wish I had this information last month. I took the 997S to Porsche to have the battery changed out and by the time they ran their "test" and had a high school student change the battery it was $385!!!

chardonet

Thanks for the write-up. So, the secret is to get into the trunk yourself for the swap out. Got it!

fhp911

hi,

same thing happened to me today -- I have a 996 GT3 ('04). Its original battery just died.
I got the Interstate MTP91 and it went in 100% easily. The car started right up.

BUT ... the 1-touch window feature isn't working anymore, and I seem to remember that the
recent article in Excellence about batteries mentioned the 1-touch windows. (I tossed the mag already, though.)

Any thoughts??

TIA, CIA, etc.,

911SLOW

^
normal since you changed battery:

press the up switch until the window is up and then hold for ten seconds
press the down switch until the window is down and then hold 10 seconds

If memory serves me right this should fix it.

John

fhp911

911SLOW is a genius, or he remembered the Excellence article better than I did.

Hold the UP switch for 10 seconds, then hold the DOWN switch for 10 seconds.

Presto !!

wogamax

I did an MTP H7 last week. I still plan on introducing the car , but wanted to contribute:
A - H7 was bigger than what came out, by 1-2 inches
B - It weighed the same ~43 pounds

fc-racer

The MTP-91 battery is the same dimensions as the factory battery and weighs less. The MTP-91 is 36.7 lbs whereas the H7 is 46.3 lbs for a ~10 lbs savings.

I've been using the MTP-91 for 1.5yrs now and have been naughty in letting the battery die completely a few times. A quick charge with the CTEK charger and it gets back to working perfectly each time.

I was away in Asia for 2.5 months recently and didn't disconnect the battery. Upon returning, the battery was so dead, my fast charger wasn't able to overcome the safety circuit (didn't sense any voltage at all) to start charging.

Hooked up the CTEK for about 20mins and got enough of a charge to allow the fast charger to work. Plugged in the 12 amp fast charger for 45 mins and was able to get the car started (barely). Drove for an hour and all has been good since.

These are tough batteries!

lawjdc

Update on this thread: My factory original battery gave up the ghost after keeping the car in storage during the endless snow this winter, without the trickle charger. Not able to revive the battery, and not excited about paying the dealer charge for a new battery and installation, so I picked up an Interstate MTP-91 at the local Goodyear store.

Be sure and get the vent kit because its absolutely necessary.

The instructions given by fc-racer are correct and easy to follow. The MTP-91 is an exact fit for the 997.1 GT3, even though the Interstate website does not say so.

The original factory battery weighed 44 lbs on my scale. The Interstate weighs 36 lbs. Where else on a GT3 can you delete 8 lbs without stripping the car, and save $$$ to boot? The Interstate was $128.73 plus tax.

Not usually excited about aftermarket parts, but the Interstate battery seems like a very good choice.

deutschmick

I replaced mine with a MTP-91 in January. Instructions by the OP were very helpful.

I called several local vendors and found a nearby quickie-lube place that had one in stock. $94.95 out-the-door. No core charge and apparently no tax noted on the sales slip. The weight savings alone would have made me happy but I could not believe my good fortune on the price.

I did have to return the next day to pick up the vent kit which they forgot to include.

Greygt3

I just replaced my battery, here are a couple notes for those of you that go the Interstate battery route.

The correct battery for the 997.1 GT3 according to Interstate is MTP-48/H6.
I spoke with the Interstate people and they told me that the MTP-91 will work but this battery will need a vent kit and it isn't a DIN spec battery. It's a USA spec battery and there are some internal differences. The price difference is twenty eight dollars.

I installed the MTP-48/H6 this evening and it's a perfect fit and has the vent on the correct side with the center carrying handles just like the Mol.

tcsracing1

i too did the interstate last year. fit great and works great.

however, i put a shop rag under the hood latch to stop it from closing by accident.
When i went for a test run of the battery outside the shop, the wind caught the hood and threw it against windshield.

cost me a hood and windshield.

also had to remove front clubsport cage to access radio antenna connectors behind a-pillars to connect to new glass.......

not cheap mistake....