The inverter only inverts, meaning changing battery 12v power to 120v power for the fridge and other 120v outlets, when you have no generator or shore power(dry camping).
The converter converts 120v power, when you are on shore power or generator power, down to 12v to power lights, and other 12v items.
The CHARGER charges the batteries when you have it on and the Generator is putting out power(make sure the generator breaker is not tripped), or on Shore Power.
You also have a SHORE MAX button/setting on the Magnum info panel. It allows you to set the 'Max' amperage that the Charger can use while you have the generator running, or are on Shore Power. If you have this set too low, such as 5 or 10amps, while the generator is running, you won't get much of a recharge for the batteries, setting it up to 40 or 50amps will give you the most charge to the batteries while the generator is running, still allowing for other 120v and 12v items to be used, such as TVs, lights, etc.
I can see the "charger on/off" on my panel but it will not let me change from off to on........should I do something before trying to turn on?