I bought a battery tender for the truck. It has two batteries. I installed it on the truck when the batteries were fully charged. I then turned on the headlights for about 2 minutes to put a load on the batteries and draw them down. This was my test to see if the battery tender could bring the batteries back up to 13.5 v float voltage.
After 30 hours the battery tender could not bring the batteries back up to a full charge. I removed it and installed a MinnKota electric boat motor battery charger. Wow what a difference and the truck and batteries loves that thing. :)