You can charger the batteries with your generator, as follows.
1. Turn the Ollie batteries on if you have a on-off switch.
2. Make sure the electrical breaker to the battery charger is ON (likely located under the dinette).
3. Plug in the ground plug into one outlet on the generator. Plug the 120V power cord you got with the Ollie into the generator. (if the generator does not have a 30 amp receptacle, you may need a connector to change the Ollie connection to a 3 prong connector to be able to plug into the generator.)
Conversely,
1. If you have access to a 30 amp power source you can plug the Ollie into that power source and the on-bard charger will charge the batteries (make sure the electrical breaker to the battery charger is on.)
2. If you have solar collectors and the trailer is now in the sun, the solar collectors have wiring directly to the batteries and the collectors should charge the batteries, but at a slower rate.
I believe the procedure should work for AGM's not sure if you have Lithium batteries, as you did not indicate what batteries you have.