Posters are saying CONVERTER not inverter.
A converter changes 120 volts AC to 12 volts DC.
An inverter changes 12 volts DC to 120 volts AC. Some rigs do have an inverter/charger.
What is make and model of your rig?
Look around the power distribution panel for make and model of your power system.
Older in-expensive converters put out a steady or nearly steady amperage and voltage to charge the batteries.
The better converters have different voltage outputs to take better care of your batteries.