I used classic cheap flooded starter batteries in solar light cyclic application (95 ah maintenance free but not vrla). I noticed this phenomenon: every month or 2 months of light daily cyclic use (DOD 15% and subsequent full recharge), the real capacity tends to decrease quite, Let's say 10% after 1 month and 20-30% after few months, even if it gives a false Open circuit voltage of 13.1 v. However, an equalization charge at 15.0 v for 1-2 hours, and consequent bubbling of the electrolyte, restores the correct full capacity for the next 1-2 months. The strange thing is that the equalization only works if I previously discharge the battery with at least 30-40% dod. While it is less effective with dods below 20%. What is the cause of this periodic behavior? I thought of slight sulfation or stratification of the electrolyte. But none of these things should happen, as the batteries are charged every day and they move and shaking with the motorhome. The problem happened at the same way with 3 batteries from 3 different brands and it seems to happen only to me. The charging and discharging parameters have always been the same: average dod 15% and complete daily recharge with absorption of 14.4v 1-2 hours and temperature compensation -18mV / C and floating 13.8v. I am afraid that the periodic equalizations will dry the electrolyte that cannot be refilled because they are free from maintenance, even if they are classic flooded. Using agm deep cycle batteries this phenomenon has never happened to me and the capacity remains constant over time for the years of use. What is the cause? Why does equalization work so much better with previous heavy discharge?
