chevy 1500 p/u light for battery keeps flashing replaced battery still flashing

POSS ALT GOING BAD.INTERNAL PARTS INSIDE LIGHT REGULATOR IS FAILING

You have to determine if alternator diodes are in good condition. Test is done with an oscilloscope and monitoring the "ripples" after AC voltage is been rectified by the diodes. A complete diagnostics of charging system must be performed to determine the problem.