Many RV 'converters' aren't very good for your battery - They aren't computerized, 3 stage chargers and they will either undercharge the battery or slowly boil all of the electrolyte out of it. They were designed primarily to replace the battery and make all of your 12 volt accessories operate off of the 120 volt power . . . . which is why they're called 'converters' and not 'chargers' - Most RV's don't use their batteries much as they are plugged in 99% of the time they're being used
This doesn't apply to all of them, but a true 3 stage 'converter' would be pretty expensive ($150 to $200 or more, depending on capacity) and also pretty heavy (again, depending on capacity) as compared to a small, inexpensive, lightweight 3 stage computer charger which can be had for $50 or less, again depending on capacity
If you camp a lot and use your battery regularly, then something which is a true 3 stage charger would be a must . . . . unless your uncle owns a bettery distributorship and you can get a new one for free every year
You really only need a 10 or 15 amp capacity as that will take very good care of your battery any time you're plugged in
Don