[Joe Bob]

Multi meter time.....trickle charge the battery or replace it. Check the charge at idle and at 2500 rpms.

12.5-13 @ rest
13-13.5 @ idle
13.5-14 @ 2500 rpms

Poor man's load test with meter attached. The volts should dip to no more 10v when cranking.

You really should not run a car with a flat battery. The alt is designed to maintain a charge, it's hard on the system when it's forced to try to bring a battery up to charge. An alt is more expensive than a battery to replace.