67 Cuda No Charge

Developed a what seems to be either low charge or no charge issues this morning and wanted to see what y'all think. It's a 67 Cuda with a American Auto wire update kit in it and a power master single wire alternator. Battery only shows 11.5 while running and doesn't go up with rpm. Battery is in the back, so there is a big fuse block wear every links together from the alternator to go down to the starter to go to the rear of the car. At that fuse block coming off the alternator there is 12 volts at idle and it goes up with rpm so alternator is working. Were should I start looking to see why the battery isn't charging it's self? Battery is also pretty old and been brought back to life after sitting a couple times and was wondering if something with that could be a culprit.
Car ran fine yesterday charging normal 14 volts at rpm at the battery and went and just randomly developed when went to run it today.
Car does also have sniper EFI on it if that could be anything, but has been fine since installation over a month ago until this morning.