My battery not charging

My battery not charging light came on the other day. Had the truck taken into a shop where they tested the battery and alternator putting it under two load tests. Everything checked out that it was working properly. Yesterday driving down the freeway the light came on again with the message battery not charging stayed on for approximately 10 seconds then went away and the voltage meter on the dash resumed its normal position. About 40 minutes later the gauge dropped, the light came back on saying battery not charging. At this point every 10 minutes or so it would go off for a bit and come back on. Finally reaching my destination the light and battery not charging message stayed on and the truck won't start now. Not sure what it might be looking for ideas, truck has no after market systems installed except a lo-jack system that was installed by my finance company but has never given any issues. Ideas please!