Lead-acid cell over-charging protector circuit is shown in the above picture. The protector can prevent middle size or large size lead-acid cell with capacity between 2 and 30 Ah from over-charging in the process of floating charging (the cell provides power for the load while being charged by trickle charge or solar panel). When it is not in the process of charging, Q1 cannot conduct the electricity due to the impedance of D1. When the charging voltage rises to about 14V, transistor Q1 (2N3055) is conducted, and splits the battery current to prevent the electrolyte from evaporating, which is beneficial for heat dissipation. Q1 should be assembled in a medium size heating panel. NTE143A can be also play the role of Q1.