Pathfinder electrical questions

Hello all, I usually hang out at the Chevy board but my roommate has an 87 Pathfinder with some problems. It is a V6, Auto, and 4WD if that makes any difference.
When he comes to a stop and the RPM lowers, the parking brake light, tranny temp light, and the battery light all come on, and then go off after the RPM increases. Also when at a stop when the blinker is on the voltmeter guage goes back and forth (small amount).
My question is if it is an alternator thing? Or could it be a battery? He said that the belt tension was a little loose and that the bearing was squeling a bit, even after retensioning. Is there are rebuilt kit for this alternator or is it best to replace the whole thing?
Thanks in advance for all the help.
Michael