Small questions if I may. I have been told that on idle or on revving (1500->3000 RPMs) a voltage greater or equal to 13.8 to 14.4 could and should be achievable ( no higher ) . My battery died most recently .... The voltage read at the new battery at idle is 13.55V ; Even if I am revving above 2000 ---> 3500 RPMs that voltage never changes - it actually sometimes drops to 13.45V at times while revving. Is this abnormal and should it warrant a closer look at the alternator , perhaps a rebuild ? Any and all insights would be so very welcome. Thank you .

 

How did the battery die on you? During regular use or did you leave the car parked for a few days and came back to a dead battery?

 

I left the headlights on for 5-7 minutes (max) while waiting to pick someone up. Nothing more was on . Car was off of course ..... Thank you for all insight .....

 

As a battery ages the level it will accept as/for full charge declines.

Generally, anything above 13 volts indicates that the battery is being charged.

Check the battery "float" level, no load, engine off, minimum should be 6x2.15, 12.9 volts.

 

With new battery?

Did you clean/burnish battery connections and new battery posts?

 

Hi !

My old battery died after just leaving the lights on for 5-7 minutes…. But then the voltages I mentioned above were with the new battery in place…. hence I got curious about the alternator output as well, and so the story began !

 

My alternator outputs a consistent 13.65v (at idle and doesn't go up with higher RPMs) which seems ok for a 964 based on forum searching I did a while ago. I know Adrian S offers >13.8v in his book, but LorenFB had some other info that a 964 alternator should put out a bit lower voltage of around 13.6 (Adrian and Loren went back and forth on this in an old thread). Regardless my car runs and starts fine and I have never replaced the alternator.