Rayarmour

My wife was out teaching my 16 year old daughter how to drive my 2002 Explorer. 75,000 kms, yesterday when the radio went dead and the car lost power. They managed to get it around the corner safely and called me on the cell. They turned of the car and it would not start. Battery dead.

I went out and put my boat battery in the car and it started and ran fine. Got it home so I could have a look.

Voltage across the battery was 12.5v and 14.1v when running. No warning lights, battery gauge on dash is fine.

Charged truck battery overnight and it shows 13.1v. Started truck this morning with boat battery still in it and it seems fine. Battery gauge good and no warning lights. Bulb good as it came on at start up.

Turned on lights and as many acc's as possible and no dimming.

Any thoughts as to my next step. Don't really want to start replacing battery or alternator if they are not the problem.