...How Many years on the Battery? As You Suspect, sounds like the Battery is going Bad, 'Shorting' Inside. Has the Battery ever been allowed to go 'Dead'? When this happens, the Battery starts to 'Eat' Itself, Up. Destroying itself. Even if the Battery is Not Very Old. The 80+ Amps could be the Voltage Regulator 'Trying' to Charge a Battery that Can Not 'Take', and 'Hold' a Charge. What Happens when the Headlights are turned On HIGH Beam, while Idling? They Should Be White!
I don't think it's the Amp Gauge. Could be the Regulator. Perhaps test the Battery in another vehicle. If You suspect Voltage Regulator, Your Chance to change-over to a Alternator with a Internal Regulator.
The Automobile Battery Must do 3 Things.
Take a FULL Charge.
Hold a FULL Charge.
Deliver Maximum Volts at Amps, Current On Demand...for 3 to 5 Seconds! Any Longer and you're Burning Up The Starter Motor.
That's All I Have. Good Luck.
MJ