Charging Lead Acid Battery Basics

When charging a battery, one’s goal is to reverse the chemical reaction that has occurred during the discharge process within the battery to extend the useful life of the battery. In the case of a lead acid battery, the chemical reaction is reversed to re-charge the battery by applying a voltage to the terminals of the battery.

Charging of a lead acid battery can be done in various ways:

Constant Voltage

Constant voltage charging is most commonly used for a sealed lead acid battery. The initial charging current in a constant voltage battery charger is limited by a resistor. Figure 1 below shows the charging over time for a constant voltage charger.

Figure 1 Credit BB Battery

Constant Current

Constant current battery charging can be used is charging multiple batteries connected in series simultaneously. An example of the charging circuit and curve can be seen below in figure 2.

Figure 2 Credit BB Battery

One should use caution when using constant current charging in order to ensure that after the battery has reached a full charge to remove the battery from the charging circuit. Overcharging can occur and can damage the battery and/or reduce the useful life of the battery.

Taper Current

Taper charging of a battery is one of the simplest charging circuits for charging the lead acid battery. See Figure 3

Figure 3 Credit BB Battery

In this method of charging, the charging voltage goes up while the charging current drops gradually as the charging of the battery continues. This is not the best way to charge a lead acid battery as it can have adverse effects on the life cycle of the battery. This type of charging should not be used on the battery once the battery has reached full charge as there is no regulation in current and voltage output of the charger as this can result in an overcharge.

Multi Stage/Smart Charger

In the multi stage charging of a lead acid battery, the charger goes into a bulk charging state where the current and voltage are at a higher rate to get a majority of the battery charged. The next stage of the charging process is also known as absorption charge. In this stage, the battery is charged with a steady voltage and a decreasing amount of current. Once the battery is nearing the end of its charge, the charger switches to a float or trickle charge. The voltage remains at a constant and the current is very low in order to get the battery to maximum capacity. The last stage can also be used to keep the battery at a full charge for a long period of time.

See below links for various lead acid chargers and IC’s that Digi-Key has available.

Lead Acid Battery Chargers
Lead Acid Battery Charger IC’s