way you will get the house battery to pass it's full current potential is if you had zero impedance between the two sets of batteries and that's not going to happen in your situation. Make sure the battery is big enough to handle the load and use a battery combiner. IMHO. Also, if you use a combiner and not a switch you don't have to run a charge wire to keep the battery charged because the combiner doesn't have to be at the load end. The combiner should be sized to your maximum possible charge rate and then about 50%. Once again, IMHO. Good luck with your project.