Exactly how was it tested?  The voltage test with the lights on and engine
idling doesn't measure the maximum output of the generator.

You need to find out how many amperes the generator is capable of
producing.  Get a Sun VAT-40, put the amp probe on the generator
output wire (with the arrow pointing away from the generator), connect the
big clamps to the battery posts, make sure the ammeter is reading the
middle (0-150A, if memory serves) scale, start the engine, increase rpm to
2500, and crank the load knob to the right while watching the voltage and
amperage meters.  Keep increasing the load until the voltage drops to
about 12.2 volts.

On a car like a Maxima, you should get 80 or more amperes before the
voltage drops below 12.2 volts, but check the specification to be certain.
If you're not within 80 percent of spec, you have a problem. Check the
cheap stuff first, like engine ground connections.

Some generators are controlled by the engine control module, and a bad ECM
ground can cause the generator to malfunction.

While you have the VAT-40 connected, twist the selector knob and check
for A/C pulses, in case the diodes are damaged, usually a result of
connecting jumper cable backwards momentarily.