996 battery/charging

I have a 2001 996 Carrera 2 cabriolet it has started to seem a little slow truning over to start and I am concerned there may be a battery or charging problem. The voltmeter sometimes sits asa low as 10 - 11 volts. Can anyone tell me what volts it should read when key turned on pre starting the engine, when engine started and when running warm ? And can I easily tell if it is a battery or charging circuit problem ? Thanks

Hi, Can't vouch for what the voltmeter will read on crankup/turnover (as my own car is not here!), but upon start up once running it should read 2mm below the 14 volt segment to represent the 13.8volt charge from the altenator. When cranking over it will be significantly less as the starter motor draws huge current from the electrical system. With the lights/heaters/wipers/heated rear window etc on blazing away on a dark rainy winters night there may be a slight drop on this but shouldn't be much below 13 volts I would say. Certain ECU's need a minimum voltage on cranking speed in order to fire the engine, not sure if the 996 uses this principal. When the engine is switched off, there will always be a drain on the battery from alarms/immobilisers etc. Maybe someone will correct me on this but I think more than 2 milliamps will cause a battery to discharge prematurely. Get a decent honest garage to do a charge/voltage leak test. They can also tell you the condition of your battery. Regards, Ian

Pls read the battery thread within the 996-FAQ sub forum and all your questions with be answered.

Thanks for that - but things have escalated since yesterday. Car was sluggush starter again this morning, did a 25 mile run. Parked. Tried to start it again immediately. Battery dead.

Have you read the FAQ thread? How old is your battery? 95% chance its dead, 5% its something alternator related. A brand new fully charged battery will post 12.2v (when you put the key in). During driving the voltage meter will read the voltage coming out of the alternator - around 13.8v. It might be higher if the batt is flat and its taking a big charge. A 20min drive is not enough to charge a drained battery - it needs a good few hours or overnight on a good trickle charger. A batt that has gone completely flat 2/3 times and is a few years old is dead to the world, replace it.

Yes I read the FAQ thread. As far as I know the battery is the oringsl 2001 fitted kit. so I agree the fault is most likely with that. currently googling a replacement price. This is the first time it has gone flat.

Most batteries last c.3ys, but some last 1yr, or 5yrs. The year the battery was made is stamped on the lugs (month & date) so maybe have a look if you want. There are lots of threads on here about other batteries to buy. The official porsche one is actually quite good, but expensive. Bosch Silver and Varta also highly regarded. Costco sometimes stock suitable ones, and "German, Swedish & French car parts" can get them in. Some people go for the halfords one, based on the principle its guaranteed for 3 (5?) years so they will just return it if/when it dies. Personally I cant be bothered with the hassle, so went for a bosch silver. Also consider buying a decent trickle charger. Ctek 3600 is a good one, but there are others as well (search on here for trickle chargers)

Sadly it turned out not to be the battery, it was the alternator. Replacement supplied and fitted at Porsche centre = £500. But thanks for the info on batteries Tonym