How do i test to see if the Alternator is bad. How do I replace it if it is? How long do they typically last?

 

Easiest way is to purchase an inexpensive Battery Monitor (Equus) for about $15 and plug into cigarette lighter.

Check voltage output. It should be about 13.5 V at idle w/ no load and fully charged battery.

If 1500 rpm output voltage is below 12v w/ a significant load (headlights on and heater blower wide open), then alternator is not putting out enough current.

Alternator can also be removed and taken to an Auto parts store for testing.

Alternators are very durable but do fail.

Make sure battery cable connections are clean and secure, and battery is good. Battery can be tested "in the car".

good luck