It's always best to dedicate a charger to a particular bank. Many use Marinco's Guest marine 12/24V chargers for the chassis. The charger of choice within this product line is (CLICK HERE). There are bi-directional charging relays that could work if you have a single engine alternator. The downside of battery combiners is they would tie multiple alternators together, which I would not recommend. BTW, if you install one it would be best to plug it into an outlet that is dead when the engine is running. I say best and I haven't done so yet. Too many things on my list.