Car turns over and will not start

Won't be the ballast resister as there is none. The wiring looks like painless. It has the fuse box inside and no bulkhead connector s its just one big roll of taped wiring going into car through a grommet. As far as what I'm running..... its a Mallory distributor, Mallory coil, massflo fuel injection with aeromotive access. I bought this car a few years back from one of our members to use while I was building mine. It ran fine until last year when it started to die after 3 or more miles of cruising. Checked battery today on the bench ...it was 100 % when taken out on Tuesday. Now sitting on bench shows 75. Can it possibly be a bad battery