20 6V Battery Charger Circuit for Lead Acid battery

This simple charger is good for 6V lead acid batteries.The main part of the circuit is the LM317 regulator IC that limits the output voltage based on R1 and R2 values. The charger automatically turns the supply off when battery reaches its full charge voltage. It has a led indicator that turns on when the battery is fully charge thus help you when are you going to remove the battery from the charger.
charger schematic diagram
Part List:
D1, D2, D3, D4 - 1N4001, 1N4004 or similar diode
Dz - 1N5235B or any 6.8V zener diode
C1 - 1000uF electrolytic capacitor rated min 16V
R1 - 12 kilo ohms 1/4W
R2, R4 - 2.2 kilo ohms 1/4W
R3 - 390 ohms 1/4W
LED - 3mm or 5mm Red or any low power LED
Q1 - 2N2907, 2N4403, CS9012 or similar PNP transistor
Q2 - 2N2222, CS9013 or similar NPN transistor
LM317 - any variable regulator IC
Bat - 6V lead-acid battery
Transformer - 110V/9V-0-9V or 220V/9V-0-9V center tap transformer
LM317 pins
PNP transistor pins
NPN transistor pins
Note: If you need a more improve charger with current and voltage control, try to modify the automatic 12V charger circuit.


  1. sir how to modify this circuit to charge a 4V 0.7A lead-acid battery?

  2. The easiest way to modify the circuit is just replace the diode DZ with 3.9V zener diode.
    This simple modification is enough to charge your battery but it lowers charger efficiency (no big deal).
    See also the 6V solar charger replace the Dz also with 3.9V zener. It’s the simpler version of the charger above.

    1. This modification May damage Thé zener after a while. R1 and R2 must be rearranged to give about 5V (check the batteries max voltage )


  3. what is the purpose of Q1 in this circuit?

  4. The main purpose of Q1 is to make sure that the charger is more sensitive and cut off the charging if it senses that the battery is fully charged. Without Q1, the circuit still works the way it is designed but there is a chance that it will take some time before it stops the charging, thus might damage your battery. But you don't have to worry because the two versions are working fine.

  5. what is the current rating of center tap transformer...

  6. The transformer rating is dependent on the size of the battery. A 10VA transformer or 1A current will do. Just take note that its useless to size up your transformer above 1.5A since the maximum current that your regulator can control is 1.5A max only.

  7. can I use 9014 or BC548 transistor for Q2, and without center tap 9V 0.5A transformer?

  8. 9014 or BC548 transistor for Q2 is okay. Or any NPN transistor of similar specs.
    For your transformer, convert it in full bridge type, meaning you need two more diodes (4 pcs of diode D1 in total). Just see the AC-DC converter on how your 9V transformer with no center tap is assembled.

  9. what is the purpose of R4 2.2 kilo ohms resistor?

  10. The main use of R4 is to make sure that the base voltage of transistor Q2 is 0V when the battery is not fully charged. It will ensure also that the charger will not turn off unless the battery voltage reaches the full charge state.. But you can remove it if you want with out any bad effect to the charger.

  11. I want to charge a 6V battery which has 12AH. What should be the values of R1 & R2 or what are the required adjustments to this circuit in order to charge my battery.
    Many thanks in advance.

  12. Sir, thank you for sharing such an useful circuit. I have made your circuit. but the problem is I had to remove R4. bcoz it won't let turn on RED LED when battery reaches full charge. Moreover I want to add an extra LED for charging indication. In that case what should I modified in this circuit ? And can I connect this charger to the battery all time?? Please let me know.

  13. Good Explanation

  14. I have some 2V sealed lead acid batteries but can't find a charger for them.
    Can anyone help with some suggestions?
    Thank you,
    Tom Peterffy

  15. dear sir, please help me to modify this charger to 12 volt charger, thanks before
    fredy g

  16. i need 4 volt bettry charger circuit like that plz help me

  17. Can I use 12volt dc 600 mA transformer and then collect 9 volt using 7809 transistor and then start to make the circuit?? Will there be any problem if I use so??