Can i charge 12v lead acid batter from adapter?

can i charge 12v lead acid batter from adapter that is rated as 12volts3.5 Amps? by directly connecting positive to + and negative to - ?

and how will i know my battery is fully charged?

i guess you need 12v and around 10-20 AMP to charge a battery.

3.5 AMP is way too slow.

ya but battery is 12v 3amp h..

motorcycle battery


I was wrong last time. My own UPS has a 6Amp charger. So i guess you should be able to do that. However, do not charge for more than an hour since you will not have any protection circuits.

, but one thing is concerning much voltage shouldmy charger output for a 12 volts battery,,?

and when should i know my battery is fully charged?

heard when it reaches 14.4 volts its fully charged?

also since my adapter is capable of delivering currents upto3.5 Amps but how could i limit it to say 300mA s i trickle charge it for 10-12 hours...

can someone tell how to controle the current?

13.8-14.4VDC depending on charge mode and termination.

A Lead Acid battery is composed of serially connected cells. Each cell has a nominal voltage of 2V. When fully discharged, the cell voltage is around 1.8V and when fully charged, it is at about 2.2 - 2.4V, so a 6-cell lead acid battery is at 12V nominal but when it is fully charged, the voltage is about 13.5-14.4V

No battery is perfect or ideal device, and it has an internal resistance which increases when battery is charged and it decreases when battery is discharged.

Now when you connect a discharged battery to a charger, the battery's internal resistance is very low. By Ohm's Law (V = I x R), a current starts flowing into the battery. This current is very large since the internal resistance of battery is very low. If the charger is not able to limit this current, the battery will draw many tens of amperes.

As the battery charges, the internal resistance increases and thus the current which battery draws from the charger decreases automatically. This current will keep flowing into the battery untill the battery terminal voltage becomes equal to the charging voltage (applied to battery by the charger). This implies that the charging voltage should not be more than the 2.4V x No of cells in the battery (14.4V in case of a common 6-cell battery). If you use a 16V charger, then battery will never reach 16V but will keep drawing current from the charger because by the chemistry of the battery, it can not reach more than 2.4V per cell.

It is obvious from above discussion that:

1) Charger should be of constant voltage type with V=14.4 Max for a 12V battery.

2) Charger must have current limiting (The max current should be AH Capacity / 10, however it depends upon battery)

3) A 12V charger can not fully charge a 12V battery. You need 2.4V / cell as charging voltage in order to fully charge a battery.

In your case, you can charge a 12V battery from your charger but it will never fully charge the battery.

Regarding trickle charging, don't worry about it if you fulfill the (1) and (2). This is because as the battery gets charged, the current will automatically reduce.

The above description is for a very basic charger, there is much more to battery charging.

now it makes much sense.

one thing more what if i use conventional dc adapter non regulated.. at 12 volts unloaded its output was 19 volts,, never checked it loaded,,

tha above transformer based simple MW adapter has max current at 350 mA max,,

will it make a ghetto charger?

if i constantly monitor battery voltage and other things manualy ,,since there is much to a charger then jus pumping current in it...

and how to limit its current cause i fear it will draw many amps if i connect it directly,, ?here is the source for all this discussion.. this instructable has been actually doing this ,, but i m too skeptical ..i forgot this link

What size of battery you want to charge with this tiny charger? With this type of adapter, the output voltage reduce when there is load. Also it can not provide more than few hundred milli amperes.

i want to charge 12volts 2.5 AH bleads acid battery, the onewhich needs regular water top ups..

i forgot to pot a link in earlier post.. re posting it..

[quote=“jhagra, post:11, topic:16657”]

i want to charge 12volts 2.5 AH bleads acid battery, the onewhich needs regular water top ups…


350mA is way too less current to charge a fully discharged 2.5AH battery. You need a charger with at least 1A current.

This MW type adapter has unregulated output voltage and the voltage will drop drastically if a discharged battery is connected to it, even to the extent that your MW adapter may burn by overheating since it has no regulation.

yes you can charged your battery 12volts and 3.5ampare