I just had both batteries changed, also changed out the positive cable that goes between both batteries, and starter. The battery light on the dash stays on. I had the new batteries and the alternator tested and they are all good, so why is the battery light still on?

Clean connections on both ends of the "B" wire, going from the alternator to the fuse box, and to the alternator. Also, clean the connections to the 175A mega fuse on the end of the fuse box; afterwards, apply dielectric grease. I would also clean all grounds going to the frame. I use 240 grit abrasive cloth.

Take a multimeter and test the regulated battery voltage, across the battery terminals, while the engine is idling. It should read 14 to 15 volts. If the problem persists, after cleaning all connections, there's a problem with the alternator. In that case, the brushes may be worn down too far. Replacing the external brush/voltage regulator assembly is easy to do, using a Torx 20 bit. It costs about $50 at Autozone.

I believe it may be Brush/Regulator on back of alternator as well? Good Luck