I have suffered a premature failure of my deep cycle gel batteries. 5 years, 320 discharge cycles to not less than 60%. A small number of discharges to 40% and one accidental complete discharge. The batteries have always been on intelligent charger set to the recommended settings. Loads are only infrequently more than C/100. The batteries have essentially all gone to a high internal resistance state and drop below 9.5V at an indicated 18% discharge. Fully recharging gives me a calculated CEF of 95% which might give some clue to the failure “chemistry”. This is a boat installation where the batteries are rarely fully charged. Solar + wind is topping them up from 60-80% pretty much every couple of days day. However they are only occasionally fully charged when on shore power. Does anyone know if my premature failure is symptomatic of this usage profile and if so, what replacement technology might be best (Lithium would be out of the question price wise).
