Possible Battery Problem?

OK here is the skinny.
83 750 twin hasn't really ran right in the last couple of years. Hard to start and then hard to get to idle till it is really warmed up.
After a ride Saturday night where the bike would sure then fallback then surge and fall back I decided I needed to check the synchronization of my carbs. But something in my head said it might be electrical. I started the bike and warmed it up, got the multimeter to check the voltage and amps going into the battery. When I undid the battery cable the bike instantly revved up and settled into a nice idle, I touched the lead back on the battery and it dropped and got to running rough again, pulled it off and it cleared itself up again.
Am I crazy in thinking that I have a cell going/gone bad in the battery and it is scavenging juice from the motor to try and fill the battery?

What was the meter reading when you had it hooked up?

About 12.5 volts, I never got an amp reading on it.

Fully charge the battery, and take it to the bike shop for a load test. They will put a resistive load across the terminals and determine if the battery is good or bad.

When you disconnected the battery cable, the alternator electrical load was removed letting the engine rev higher.

Just went and looked at the battery. The battery had a crack and a dry cell. Oh well off to the battery store I go. thanks guys.