Make SURE you have a good ground from the battery to BOTH The frame and the engine block, and prefferably a ground strap from the block to the frame.

If the alternator indeed is producing amperage when tested, but the battery is not getting a charge, the problem is likely in the grounding between the frame and the motor.

With the engine running, pull one of the battery cables off battery. If it dies, you are NOT getting power from the alternator.

Scott