Maybe run a multi meter on your batteries while vehicle is running. I recently had incredible situation where the inbuilt regulator was stuffed on my altenator which was charging at 17.5 V. Luckily I twigged and made it home, with lights, radio, aircon, etc. on , to draw power down, then fitted a new altenator.
Did blow radio speakers and coil lead into dizzy looked bad, so I replaced all leads, dizzy cap and rotor. Phew!.