MitchB

Haven't driven the TT all winter (not much anyway..). I try to start it once a week or so, but it went abt a month. It started to feel very reluctant to spin the starter - felt very much like a low batt charge. An overnite charge and it was fine - till a week later. Same symptom.

Got out the meter. Voltage at the battery with motor running is just a hair below 14 volts. Battery before charging - abt 11.8 volts.
So - I charged the battery until the reading at the battery posts matched the charger - 13.8 volts. Checked after removing charger - 12.3 volts. Checked a week later - 12.2 volts, so no loss over a week.
Battery is original. Car has 19K miles. No other symptoms. Terminals are clean, is the battery bad?

slant911

Probably a bad battery. Sounds like it's not holding a charge very well. Surprised it even lated this long being the original battery. Go to Big O tires or whoever else in your area that carries the Interstate batteries. They have a direct replacement and it is reasonably priced.

MitchB

So how do you like working for Interstate?

slant911

Not sure what you are assuming or saying Mitch but I don't work for Interstate. Just a happy consumer.

mdd

I had the same battery symptoms that you describe except that it ended up not starting on Friday. Replaced it Saturday and all is good. Costco had a replacement for $39 after the $10 instant off. 3 year free replacement and 100 month prorated warantee.

MitchB

Just sounded like you were pushing them... The problem with text vs. speech.

Not convinced it's the Batt. It's a 12 volt batt, and it holds 12 volts - isn't that what it's supposed to do?

slant911

Actually a full battery should be upwards of 13V. If your battery is sitting at 12V with nothing on car not started it is half dead already. And 12V sitting still is a far cry from under load where failed cells show their ugly heads. The charging system should be pushing almost 14V (13.8 as I recall).

Other reason is pretty simple....I'd bet no one on here has their original battery still from an 02'. They just don't last that long.

ltc

I just replaced the original OEM battery in my 01, 5150 miles.
Went with another OEM Moll battery FWIW.

ltc

Have you removed the battery and looked at the cells and electrolyte levels?
Have you measured the specific gravity of the electrolyte?

1AS

I still have mine form February 02. Seems to be okay, but I am religious about using the Porsche trickle charger whenever the car sits for more than a few days. My 99 Boxster went to the summer of 07 (same technique, but longer periods of no use) before the battery failed all at once. AS

whiteturbo

You can take the battery to most parts stores and they can check it.............But i would bet it is bad. I replaced mine last year and it is a 01. I also replaced it with a Interstate. I don't work for them either nor do i want to.

porschedude996TT

The old rule of thumb was that during cranking the battery voltage should not drop below 8.6 volts. If it does then either the battery is defective or the battery is too small. Newer vehicles like higher voltages during starting because they are electronic ignition systems and all the other load that exists during the cranking and starting. A freshly charged 12 volt battery will be about 13.75 volts and start dropping on the 100th scale after you take it off the charger. If the battery is charged and it indicates that the electrolyte is in the green zone on the Hydrometer and the engine does not spin quickly, then my guess it is the Battery has sulfated plates and the will reduce the effective capacity.

Wow, that is a cheap price on the battery from Costco. I bought mine from Sears, Diehard and it was bigger than the standard battery and it was $119 with the core exchanged. I have had Interstate Batteries in Porsches and they have serviced me well. They are a very good quality unit and the support is not bad either.

The real secret with these 996tt's is using a battery tender when you don't drive the car every day or so for enough miles to sufficiently charge and warm the engine and get the engine oil up to temperature to drive the fuel and water out of the oil . It is not worth firing the engine once a week and thinking that the battery will charge and replenish the energy that you lost during the week and the energy used during your starting event. Better to just leave the battery tender on and not fire the engine. If you start the engine and drive it so infrequently, then you should use so fuel stabilizer in the tank and keep the tires off the ground.

MitchB

KW -
Good advice all around. I have seen the 8.6 volt figure elsewhere, but was looking here to see if these cars had differing criteria.
I do have a battery tender, but didn't use because I thought I'd drive it more. But your advice is sound. Seems odd that I could leave such a wonderful car just sitting...

I will most likely be getting a battery from the dealer. Around $180 with PCA discount. More money than I'd like to spend, but with car for sale soon, want to keep it as original looking as possible. Besides, the factory battery lasted over six years in a car that wasn't driven much - would another battery do significantly better...?

whiteturbo

My dealer in Charlotte NC replaces them with Interstate. I would think they have the OEM for warranty replacement. I bought 3 OEM's for my 930 and the last one was a Die hard and it lasted much longer than the OEM. My Oem in the 996 lasted about 5 years so they may be better now.

RacyTracy

But even then you can't always be sure. I had all the same symptoms this spring listed by the OP.....took the battery to AutoZone for their FREE test. They said it was fine....came home, reinstalled it...car still wouldn't start after driving. Just came home from the dealer after having a test done on the charging system. They said everything is fine...........except I have a bad battery. They wanted $400 for a new one.