This has not been my experience with the Genesis. The G Screen allows me to monitor the charge on both batteries independently. I will arrive at a camp spot with both batteries Fully charged at 14.2. Running led lights, charging lamps/phones, ARB frig, etc... At the end of a long weekend camping, my house battery will often be a little low, but starter is still charged (12.7). I do intend to add solar panels with a charger, to extend my base camp time. Only needed since I started to use my ARB frig. Before that, I could go a week without starting the vehicle. I'm sure a multistage charger would improve my battery life, and is a much better solution. Up to this point, I have not felt the need for this upgrade. The smart Isolator built into the Genesis, (it automatically handles all charging functions), meets my needs.
If you are considering the Genesis duel battery system, their site has lots of good info. The owner takes calls, if you have questions.
I hope this helps.