The overall reaction of the charging lead acid battery is the reaction of lead [ions/atoms] in lead sulfate to form at the cathode and at the anode. This is a non-spontaneous redox reaction which converts electrical into chemical energy.
• It is because the reaction will not occur on its own: heat or a potential difference do not need to be provided to cause the reaction to occur.
• It is a redox reaction: it involves the transfer of from one chemical to another.
• It converts into energy as the chemical reaction creates a potential difference across the electrodes.