Flashing battery light

[Jeff Mann]

This is a rewording of another post, but here goes. My battery light flashes at certain RPM's. I have changed the alternator 2 times but the problem is still there. The truck runs smooth but when I punch the throttle at 60 mph and start to climb the battery light flashes a few times and then goes off. The truck never skips a beat but the amps drop slightly. The same thing happens when sitting still and I rev the RPM's up. Has anybody ever seen or heard of something like this before?. Please help.

[bigtruck21]

is the battery old, or maybe bad?