Age old question...Bad Battery or Bad Alternator???

I will complete the testing you listed tomorrow....One question in regards to the Volt. Reg., the right bolt connecting to the firewall appears stripped. It will not tighten only loosely snug then spin and resnug. The VR is tighly mounted due to the left bolt being very tight to the firewall. Could this be my culprit? Any ideas how to fix the stripped hole in the firewall. I doubt I could drill the VR mounting larger w/o cracking it in order to use a larger bolt.