I am getting tired of REPEATING this this. It has been covered in at least a dozen different posts in the past 3 or 4 months. Here it is AGAIN !
Vehicle alternators/charging systems are NOT a good way to charge a "house" battery bank. You just proved that ! Heavier gauge wiring will help a little but not a lot. With out going into the specific details, if you want to PROPERLY charge a deep cycle battery bank you need to do the following:
- Install a DC-DC boost converter between the vehicle battery and the house battery. Its output should be set to about 16V. (These are cheap on eBay of Amazon. No housing or wiring;
Don't believe the maximum amps. It you "push" it hard, you need a housing with a fan.) - After the boost converter, install a deep cycle solar charge controller (An inexpensive PWM model is fine.)
- Connect the output of the solar charge controller to the battery bank
