4v SLA battery charger- can i use nokia 5.7v 800ma charger

robotsmani said:

The battery voltage showing 3.65v. After bought this i have not used. it was unconnected for 6months i think....

Click to expand...

That means the batteries are seriously discharged. Bad news: A SLA that starts out fully-charged will (barely) survive sitting disconnected from any load for six months. Six months is about where the self-discharge depletes the battery. A discharged battery sitting around forms hard sulphates on the plates, which greatly reduce the capacity of the battery when you finally get around to charging it.

The only way to keep unused SLAs from deterioriating during periods of non-use is to follow the manufacturer's recommendation and keep them on "float" charging. I suspect yours are junk.

The answer to your question about overnight charging is in my previous posts. Please read them...

Thanks Mike...
The batteries are chinese and it is very cheap. 2 batteries/$. I will buy some new

one battery successfully charged. one more question...can i connect the battery in series and charge...say for 3 batteries in series makes 12v, set the power source voltage to 14.5v and i think current limit is same 100ma. Is it possible?

The only time connecting batteries in series is a problem is if they have a different stage-of-charge or different capacity. Series connected batteries should all be new, and fully-charged when initially put in service.

SLA battery

Don't overcharge and monitor its temperature and charging current as these SLA cells will vent when overcharged.

See attached photo when a 12V7Ah cell was put on a 70 Amp charger to prove a point.

oops, it is scary....now i scar to put the charge on over night....

Bear in mind that this battery was charged / destroyed at 70 Amp AC current.
I just wanted to see what would happen and did that test outside.

I had heard about these SLA's venting and decided to blow one up.

In your case charging at 100 mA just keep an eye on the charging process.

When the battery starts crackling, that sound like stress and pressure building up in the cell blocks.

Early warning signs are the smell of sulphuric acid ( very nasty ).

You can see that battery venting on my YouTube channel.

one of my 12v 7.2AH battery is not showing any voltages. Then i tried to recharge with LM317 circuit. After several hours it is charged by some 6.7v, but when i measure the amp there is not Amp there. Is this mean this battery is dead. This battery is from my UPS, it was not working long time, so i want to find it is a battery prob or the UPS.

Two possibilities: (1) chronic overcharging by the UPS (electrolyte dried out). Root cause: charge voltage too high.
(2) chronic undercharging by the UPS (the battery is sulphated). Root cause: charge voltage too low.

Read .

Thought to post a pic of those 4v batteries



One question i want to charge these 4 batteries at a time. Can i connected it in parallel and increase the current of the power supply? Charging the batteries one by one is a pain

Charge them individually once. After you have proved that they are useable (i.e. no shorted cells, have useful capacity), then you can charge the 4V batteries in parallel with other 4V batteries. Obviously, you cannot parallel a 12V battery with a 4V, and the charger must be modified for 12V batteries.