HA12 Equaliser – battery balancer – The HA12 battery equaliser is used for batteries which are connected in series to keep the voltage of batteries equal when charging or discharging. When connected in series battery voltages will vary due to the differences in cell chemical composition and temperature, each battery’s self discharge rate will  also be different. These differences will cause battery pack to become unbalanced, this imbalance will result in undercharging and overcharging of the batteries resulting in sulfation and premature corrosion of the plates. The voltage difference will increased over time and subsequent charging cycles. This will result in premature failure of the batteries.