Some people do it quite often, and my Magnum controller can remind me every 30 days.
For no reason other than that seems excessive to me, I do mine once a year during the spring. But I upgraded my coach when I first bought it and put in another set of house batteries increasing my total capacity, so I always typically have more than enough battery capacity for our travels.
DaveB, Raleigh, NC
2015 Tiffin RED 33AA, w/Honda CRV
VMSpc, Magnum BMK/ARC50