the trojans in my cargo toy hauler trailer were installed in 2004, went to in-laws in 2014, and just this year are due for replacement. the SG is down to 1.25 probably could get another year out of them.
Trojans in my big trailer were installed in 2009, just equalized today and the SG is 1.28 on all cells in all 4, still good to go.
and these batteries get used and abused. the cargo trailer batteries often were discharged to 25 percent SOC around 300 + times total. Big trailer often sees discharges below 50 percent before recharging when dry camping.
On my cars, my 2004 duramax batteries went 10 years before needing replacment, my 97 Mercedes sedan needed a new battery in 2012, 15 years. My 97 Mercedes roadster PO replaced the battery in 2006 and I replaced it again last year.
Monitor SG after equalizing, that will tell you when you need to replace them.
2011 Keystone Outback 295RE
2004 14' bikehauler with full living quarters
2015.5 Denali 4x4 CC/SB Duramax/Allison
2004.5 Silverado 4x4 CC/SB Duramax/Allison passed on to our Son!