Second battery
Our camper has only room for one group 24 battery. A few years ago I added wiring and a multipoint switch for an additional battery to go ahead of the rear wheel well but have not used it until now. ...
Forum Discussion
The age and brand of the batteries ideally would be the same, otherwise they will charge and discharge at different rates.
The distance between them can be compensated for by wiring them in parallel correctly. The easy (and incorrect) way is to run a positive and negative cable from your existing battery to the added battery. This will cause voltage drops to the remote battery, reducing it's capacity and life. It is only slightly more difficult to do it correctly: run a positive and negative cable between the batteries, putting them in parallel. Now take the ground cable for the charge/load to one battery and the positive charge/load cable to the other one. The voltage drops are now matched across them. This is proper way to do it, even if they are sitting side by side, though you don't often see it done that way (on purpose) in the RV industry.
In your case with the extra battery in the truck bed, you need a way to go back to the original when the truck bed battery isn't in the system (camper off truck for example).
The distance between them can be compensated for by wiring them in parallel correctly. The easy (and incorrect) way is to run a positive and negative cable from your existing battery to the added battery. This will cause voltage drops to the remote battery, reducing it's capacity and life. It is only slightly more difficult to do it correctly: run a positive and negative cable between the batteries, putting them in parallel. Now take the ground cable for the charge/load to one battery and the positive charge/load cable to the other one. The voltage drops are now matched across them. This is proper way to do it, even if they are sitting side by side, though you don't often see it done that way (on purpose) in the RV industry.
In your case with the extra battery in the truck bed, you need a way to go back to the original when the truck bed battery isn't in the system (camper off truck for example).
