Alternator light

[steve349]

light randomly comes on, seems to happen most when its raining, could be no correlation... I had the alternator tested at auto zone (i heard most members think they undertest) they said it was good, noticed my s belt was missing a rib replaced that and the tensioner. belt still seems a little loose all the pulleys seem firm though. all the uptop battery connections are solid. would i be getting this light if a battery was going bad? If it helps I also seem to be having some cold start issues.. if i don't leave the blockheater on in less than say 20 degrees it turns extremley slow almost like the batterys dead. Im assuming the GPR is bad and am planning on replacing it with the stancor. Im also going to be doing the fuel filters and upgrading to a good oil to help with the cold start. But my main issue is that the light is scaring me