If it's keeping the battery charged, there's no reason to replace it. With the engine running at fast idle (1500-2000 RPM) you should be able to measure 14 volts or so at the battery posts with a digital voltmeter. Depending on the state of charge of the battery, that voltage could vary from 13.5-14.5 with no problems. Beware of a voltage below 13, it usually means the alternator is not doing its job right.
Next test- - - -also at fast idle, turn on every accessory you can- - - -high beam headlights, high speed heater blower, high speed wipers, cigarette lighter, etc. to put as much load as possible on the alternator. Check the voltage at the battery again. It should be 13 volts or more. This checks the alternator's ability to keep up with the current demand of the accessories. If the charging systems passes these tests, don't mess with it. People who recommend a super high-output alternator like a 100 amp or more have no understanding of what a charging system is supposed to do. The only reason for going to such a ridiculous amp output would be to support a mega-watt sound system, or a set of hydraulic pumps for a lowrider, or something equally stupid!
Jerry
