Lead-acid batteries, like lithium batteries, should not be overcharged or overput. However, when the lithium battery is used, it is generally combined with the protection board to achieve overcharge and discharge, short circuit and other protection. However, lead-acid batteries are generally used independently, and overcharge and discharge require human control or protection by the charge and discharge circuit inside the load. When charging the battery, the finished charger or charge management chip is generally used, and the voltage sampling inside the charger and the charge management chip generally design the overcharge protection circuit and the secondary charge protection circuit. Therefore, during the use of the battery, it is often easy to overdischarge.