12v gelled electrolyte battery charger circuit schematic

12V Gelled-Electrolyte Battery Charger

This circuit is a high-performance charger for gelled-electrolyte lead-acid batteries. This charger quickly recharges the battery and shuts off at full charge. It uses the well-known LM301A and LM350 ICs.

Initially, charging current is limited to 2A. As the battery voltage rises, current to the battery decreases, and the current had decreased to 150 mA, the charge switches to a lower float voltage which prevents overcharge.

When the start switch is pushed, the output of the charger goes to 14.5V. As the battery approaches full charge, the charging current decreases and the output voltage is reduced to 14.5V to about 12.5V, terminating the charging. Transistor then lights the LED as a visual indicator of full charge.

12V battery charger circuit schematic

12v gelled electrolyte battery charger circuit schematic


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  • krishantha

    I made this Battery charger circuit using the LM338K IC.

    1. When I use the 15V 3A transformer for this, charging current is about 2.5A (Battery is 10A)
    2. Same condition, when I use the 5A transformer for this circuit, charging current is about 2A.
    My question is, why this different?

    Thanks & Regards

  • Sachin


    I have ebike, it is 48V.

    The chargers available in market are all coming from china and they just bust out after 8 months. I am fed up of buying them again and again costing me 2,500 INR for new one.

    I thought this circuit is of help as the batteries used in ebikes are gelled electrolyte ones. But problem is that 2A charging current would take 12+ hours to fully charge 40AH battery.

    So, could you please provide updated version of this circuit with 4A charging current? I will have to build 4 chargers for 4 batteries, but that is OK I feel.



    Dear Mr.P. Marian

    Can you please give details of adding overdischarge battery protection in this circuit, as this also be very usefull for the batteries life.