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Topic: How do i charge a 12 volt Sealed Lead Acid battery?? (Read 8504 times) previous topic - next topic


I have a 12 volt Rechargeable Sealed Lead Acid Battery type FM1275C (probably Chinese) rated for 12v 7.5Ah and 20 HR charging (written as 12V7.5Ah/20HR on the battery). In my arsenal i've got a voltage regulated non PWM power supply able to supply 17 volts @ open circuit and 11.5 volts @ its peak 3Amp current (so its a 12 volt 3 Amp capacitor smoothed voltage regulated power supply). I took the battery from a portable generator. At the beginning it was able to start the generator's engine but now its not. It is currently charged at 4.7 volts and can supply a maximum of 300mA at this state.

Can you guys tell me how can i charge this battery through the power supply?   

Thanks in advance and have a GREAT day :)


If you have a 12V battery and it's current voltage is 4.7V then it is knackerd, shot, kerput. No ammount of charging is going to rescue it. It is damaged beyond repair.

To correctly charge a battery you need to charge it with a constant current of one tenth of the amp hour rate with a maximum voltage of about 14V.


You'll be lucky to get more than 5 to 10% of its rated capacity back now - you can try charging it at 14V for several days to try and break up
the sulfation crystals and you may get a bit more current from it, but nothing like its rated current.

The rule with lead acid is never discharge below 10.5V (for a 12V battery), never ever store discharged - ie charge after use,
preferably to full charge.  Trickle charge every month or two during storage.  Store as cool as possible.  Trickle charging to 13.8V
IIRC is the normal scheme (perhaps at C/30 or so).

In general lead-acid are high-maintainance batteries, but are very well suited to vehicle batteries as they always get recharged
after use to full and seldom left for months.
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