8 yrs no problem for 6 volts, been there.
Not sure about 12'ers, but mine at near 5 yrs now, and looking good.
My secret, a PD wizard conv/charger. Whatever they do, they do it right.
Rich
'01 31' Rexall Vision, Generac 5.5k, 1000 watt Honda, PD 9245 conv, 300 watts Solar, 150 watt inv, 2 Cos 6v batts, ammeters, led voltmeters all over the place, KD/sat, 2 Oly Cat heaters w/ ox, and towing a 2012 Liberty, Lowe bass boat, or a Kawi Mule.