Frontier Eats Batteries

1998 Frontier 2WD 4 cylinder, 5 speed, stock. I've had this 2 years, and gone through 4 batteries, last three replaced at no charge. All suddenly read about 4 volts, Autozone recharged, but then when put on the checking machine, all read bad, so they gave me new battery each time. When running, alternator puts out 14 volts like it should. Autozone said it was putting out 73 amps, so that was too much, as the stock 70 amp alternator should only put out about 66% of its rated amperage (does that sound right to anyone?); they said charging voltage and diodes were fine, and suggest putting in a new alternator. Does this sound like the next step, does anyone relly know?

Might want to see if there is a draw in the system witch is killing th battery. Anything aftermarket installed ( Radio? , Amp? ) If So Install Should be rechecked . If you have nothing installed after marker, I would have to say Take it to someone who knows how to check for a draw on the electrical system. I would start there gl :)