The solar charge controller limits the battery voltage to the set point voltage you choose depending on your battery type. The standard settings for charging RV batteries are Gel, AGM, Wet and Calcium which changes the output voltage to match your battery type.
All controllers above from ZS-10A to ZS-40A are now Lithium compatible with the standard 4 battery type settings mentioned and two additional settings for Lithium which are LiFePO4 & LTO. The last digit like 10A or 30A is the solar controllers limit of amperage it can handle. So a larger controller will allow you to expand your solar needs later if you choose to.