The 600 AH Bank I had in our last caravan comprised (8 x 300 AH) HiPower cells that had been in an off grid house in Dunedin for three years before I purchased them and close to seven years old when I sold the van. I performed a capacity test in September 2017 using a 20 amp load for just on 30 hours and the Votronic meter reached "0" AH remaining.
Voltage was beginning to drop off with the four pairs of paralleled cells all at 2.8v - 2.9v The battery dropped below 12 volts for the first time that I had owned it - 11.5 volts. Result - I was pretty happy that at almost 8 years old there was virtually zero loss of capacity. ( I was reluctant to continue the discharge to the manufacturers recommended minimum 2.5 volts per cell.) These cells have had a fairly easy life since I have owned them with a 13.8 volt maximum charge voltage and very seldom discharged below 50%. On that basis I am fairly optimistic that these cells I have just purchased will be in pretty good shape.