car dies

I have a 99 gtp I am having trouble keeping the battery charged. I have replaced the alternator and battery, twice. I have a volt meter and the large terminal from the alternator only reads 8.5 vdc why am I getting such a low output? And how do I trouble shoot any further in the circuit?

Welcome to AF.

Thats too low. What voltage do you have across the battery positive and negative terminals at idle?

I had between 13.7 and 14.5 vdc.

Would belt slippage or possibly a weak tensioner itself be a reason for such low output?

I had between 13.7 and 14.5 vdc.

Had or does it currently read that? Thats normal and indicates the alternator is putting out and charging the battery (or should be).

Have you checked for any battery drain or parasitic draw? Look for current in milliamperes from the battery negative cable to ground. Meter in series.

I will have to check for any sort of draw. I greatly appreciate your help in this matter. And thank you for welcoming me in the community.