experience spruce. when started I charged every day. then got my identical 110 amp battery out of caravan as spare so wouldn't be screwed when went flat, it lasted nearly 4 weeks or 3 short days!
so when carry spare I swap after 3 weeks, when I don't I tend to charge every other week. I only charge at 2 amp. so far batteries lasted 2 years, and no sign of shortening battery life.
just remember tho unless u have spare with u, or means to run off van (I know old man Harding can run his off cigarette lighter) then a flat battery means end of working day.