It is in alot of posts here, u need to look em up, I mean alot, But to help fast, Yes u can, u can put a 12 volt charger on each batt and leave em in and hooked up,of course if u gat 2 12 volt chargers.AND U can pull up 2 cars and use a set or jumpers from one car to one batt and repeat the other car to the other batt, If u only have one 12 volt charger and u want to charge both at the same time, U can pull them from the truck hook up one batt and use a jumper in parrallel and the 12 volt will charge both batts, but more slowly of course, Most people just make it more complicated than it is, OK I re read your last post, U can not hook up a 12 volt charger in series and charge 2 batts, U CAN charge one at a time with a 12 volt charger and leave em in the truck.U can purchase a 24 volt charger, Think about what u want, are U in this type of truck for the long hual, if so go buy what U need, the ultimate way is an on board charger desulphater they come in 12 and 24 volt chargers, I have 24 volt ones in my trucks I get 9 and counting years on some with proper maintenence, I am going to mount 4 12 volt desulphaters in my 925 when i get the funding and remove the single 24 volt, because it is the ulitimate , each batt is at the best it can be, If U do not have both of your batts fully charged and checked to see if they are holding the same voltage the lower one will always win and the better one will stay at the lower ones level and it will shorten there life, Many people blame the batts for failure, it is always 100 percent human error, not taking the time to understand the batts and how to maintain them, they must be cleaned and fully charged all the time for them to last...randy