Put a new battery in my Canon A1 and things didn't quite work right. It would only fire half the time and the shutter speed was all messed up. 2 seconds sounded like 1/1000.
Pulled the battery from my AE-1, put it in and everything is just fine.
Are these cameras so voltage sensitive that a slightly bad battery could cause problems? Anyone else witnessed this?
Your A1 would be approximately 30 years old. That is certainly enough time for the battery contacts to lose some of their "spring", or to be bent away from their optimal position. This may be a case where the mechanical connection wasn't complete, but a slightly larger battery compensated for the problem. Gently moving/bending the contacts a small amount might make the difference with the other, slightly smaller battery.