The last 2-3 times I started my 964, I noticed that the starter turned more and more slowly.

This evening after 4 days of no driving, I still had some juice but not enough to start the car.

Does this look like battery or alternator issue?

Thanks

 

Charge the battery and then measure the voltage across the battery terminal it should be approximately 12.6 volts dc. While the engine is starting it shouldn't drop below 9.9 volts dc. If the battery fails these tests take it to a shop for a load test otherwise, While the engine is idling measure the voltage across the battery terminals. If the alternator is charging correctly it should read around 13.8 to 14.4 volts dc. If the voltage exceeds 14.4 volts dc the voltage regulator has failed shorted. If voltage is too low, rev the engine and when it reaches 13.8 volts dc and if the rpm has excedded 1200 then the alternator or regualtor is failing.

Hope this helps
Bill
90C2

 

Thanks a lot! I'll try it.

 

Here are the results:

1) When starting the engine, voltage goes down to 9.85 (9.90 minimum suggested).

2) When the alternator is charging, voltage reads 13.60 (around 13.80 suggested).

I'm running a Optima red top and never had any problems until now. I have a 993 engine too. Next step is have someone do a load test... I have been doing short trips recently (12 miles), but it should be enough to charge the battery!?! I guess I have to drive my 911 more often!

 

You didn't mention what the battery voltage was after recharging it. If it started off lower than 12.6 that may explain why your cranking and charging voltages are both low. Short runs may be the cause for the battery to never charge completly especially if you have a lot of accessories on.