Well on my way to Wisconsin Dells with the family the low voltage comes on. I look at the meter and it's 11.8. I slowly accelerated and while under load the voltage went slowly up to 13.5. But while not under load the voltage would slowly drop back down. I figured it was a bad battery. The battery hasn't been replaced in 3 years so I figured I'd buy one on the road and replace it if the car died. We made the 3 hour trip with two pit stops on the way ( car was off for 40 minutes during stops). This morning I went out and it's dead. So I put the other battery in. Car starts right up after install. I get out close hood, sit down again low voltage light comes on... 11.6. I figure take car for a drive maybe this new battery needs a charge. Car dies, no power. So tow truck arrives after a few taxi rides to auto part stores with no luck for battery. He puts his jump box on it and it says battery has 20 volts.. Car still won't start. His jump box says it has 14 volts and the battery still has 20 volts. Alternator? Bad battery? Maybe drawing voltage at short? Sorry for paragraph. Thanks for any insight.