The controller considers multiple batteries wired together in series or parallel, with a single 12 volt output as one battery bank or a single battery.  A second battery would have to power separate circuits such as a starter battery or a separate battery for your slides. 

Charging Process

Exactly how and when Battery2 progresses through the charge states will depend on how well charged Battery1 is, how much energy is available from solar, how much the customer is using loads, etc. 

The controller prioritizes Battery1 over Battery2. If the controller can’t maintain a charge voltage like Absorption or Float for Battery1, then current for Battery2 will be reduced or will be 0A. 

For each battery, the daily charge progression ideally is:   Day Detected à Bulk à Absorption or Equalize à Float à Night detected 

With the dual batteries, the daily progression looks more like this (assuming there’s enough energy for Battery1 to progress):  Day Detected à Bulk with full available current for Battery1 à Absorption or Equalize for Battery1 and excess current used for Battery2 à Float for Battery1 and excess current used for Battery2 à Night detected 

Exactly how and when Battery2 progresses through the charge states will depend on how well charged Battery1 is, how much energy is available from solar, how much the customer is using loads, etc.