Charge both batts same time in the truck, Remove nothing , U can jump with 2 batts using 2 sets of jumper cables, 2 separate cars will do this.. Its not rocket science , LOL Never have to remove anything to charge em in the truck with a batt charger on each batt, If you had only one batt charger you could just charge one at a time in the truck, Same thing, The second batt will take some charge but will NOT fully charge so you need to move the charger to the other batt when the first one is charged, This can be done with 4 batt set ups also.
FYI, The bad batt is the one that is at the end of the charging system . Charge that one first and make sure it will take a charge if you only have one charger, The last batt is never fully charged in these trucks, therefore they sulphate first and die first. these are not smart charging systems and I don't know of any smart charging systems in any vehicles, Its like filling a pool, There is over flow to the other batts, But when they are close to charge the resistance is strong enough to shut charging down, Because to fully charge the batts in back you would have to over charge the first batt, 973 219 4499 if U have any other questions, A good running truck does not need much of a boost in mild temps to start it, AKA The guy with the little battery in the Jap truck jumping His Mil Big batt truck,