yes you can put AGM batteries in the garage
you said 'inverter'
do you have an inverter/charger combo unit
or do you have seperate converter for charging and inverter for making 120v
what make model, what charge rate ?
probably anything you have can be used, but people have a habit of using large amounts of power when using an inverter aka microwave cooking, coffee maker
then they want to run the generator the shortest amount of time
sometimes they don't run it enough, because they are not charging/replacing the used power like they think they are
