1 to 10 years depending on the quality of your converter/charger and the quality of ... well... YOU.
Took me a few years to learn all the facts.. I used to get new batteries every spring, but once I studied and learned.. My last set lasted
AGM's. 5 years
Flooded wet 9 years
Maintenance free: not really sure but about 9 years is close (They were older than the RV, RV is 9, just put new GC-2's in it last month, Replaced chassis batery a month or so before that.. Got AGM's in 2006 replaced in 2011, they were actually dead before that,, One of the reasons I'm not a fan of AGM's.)
Converter (This is important) is a Progressive Dynamics Intella power 9180 with wizard
Battery bank (Current) is two GC-2 (flooded wet) and I think 3 Group 29 Maintenance free in parallel . I have room for one more G-29 if I wish, used to have 2 G-31 AGMs and a 2 G-29s (MF) which were older than the RV.
One Inverter/converter (converter normally disabled) Prosine 2.0
Chassis battery is a group 78
I do check fluid level in the GC2s at least 4 times a year,, New I add about annually, as they age the frequency of add increases.. DISTILLED WATER only.
In the old days I used an automotive type charger on a Maintenance Free Marine/Deep cycle with a trailer and had to put new batteries in annually. Finally learned how to keep em lasting longer.. The original G-29's were from teh trailer and from a home emergency power pack.