Belt slipping?

[R-U-QUIKR]

Is it possible for a belt to be slipping without making to much of a sound? My alt and battery are new but the car is only making 11.6 volts. The belt is old and stretched to the max but is still taught.

 

[blueberry_dsm]

it is possible if the belt is old and smooth on the contact points to the pullies. otherwise it could just be a battery that just wont hold a charge, but i doubt it. my advice would be to tighten the belt a little bit more, then fully charge it. if it keeps goin down, i would suggest a new belt, i think they're around $40. if u put a new belt on it and it keeps goin down, then either the alt or bat r defective, or else (more common) there is a small draw somewhere, but to find that you might need to take it to a shop, unless you have a current draw tester. but thats just my $0.02.

 

[blueberry_dsm]

now that i thought about it more. 11.6 aint good, a dead battery is at 10.5, and a full is around 13.6. with the car running at idle, preferably warm, connect a volt meter to the battery and see if the car is keeping up the volts, or if it is slowly dropping, or stayin at 11.6. if it goes back up to 13's or even 14's, then the alt is good, if not then the alt is bad. but i think it would be a bad battery b4 it would be a bad alt, but i could be wrong.