I suspect 5-6 years might be the expected minimum... My 255AH battery bank has been running since 2009 with great performance still being observed.
You have to do your battery maintenance and not just let them fend for themselves. Having a smart mode converter/charger is a must have thing if you want long service from your batteries. This unit does most of the battery maintenance for you...
Also I follow the golden rule to never discharge my battery below the 50% state of charge which is around 12.0VDC and watch my battery fluids on a scheduled basis.
My batteries stay on my trailer the year around but I do have a total disconnect setup with my BLUE SEA battery switch arrangement. Both my trailers are connected to the garage 120VAC receptacles when parked here at my CAMP BACKYARD. I can either leave the batteries on charge from the on-board smart mode converter/charger or switch completely off-line after they get a full 100% charge state and just switch back ON every month for a few days to get re-charged. I always check the battery DC VOLTAGEs on a regular basis at the terminals when I leave them in their total disconnect configuration.
I do have a THERMAL CUBE running an oil-filled heater when the temperature drops below 35 degrees and shut off when the temperature gets above 45 degrees in both trailers so I usually just leave my batteries connected to the on-board smart mode converter/charger unit over the winter months.
The winters here in Northern Neck Virginia are not that harsh or long term. Warms up good during the daytime...
Roy Ken
My Posts are IMHO based on my experiences - Words in CAPS does not mean I am shouting
Roy - Carolyn
RETIRED DOAF/DON/DOD/CONTR RADIO TECH (42yrs)
K9PHT (Since 1957) 146.52M
2010 F150, 5.4,3:73 Gears,SCab
2008 Starcraft 14RT EU2000i GEN
2005 Flagstaff 8528RESS