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How to make a charger for a 4 volt 4.5 ah sla battery? Answered

I have a 4 volt 4.5 ah sealed lead acid battery out of a cordless phone battery backup thing and I have no way to charge it. Does anyone know how to make a charger for it or even at what voltage and amps to charge it at? Thanks.



Best Answer 9 years ago

you need to use 4.6-4.7v 1A for approximately 6 hours. i found this information out of the manual from my sealed lead acid battery charger. battery volt no. cells charge volt max discharge volt 2 1 2.30v 1.6v 4 2 4.65v 3.0v 6 3 6.90v 4.2v 8 4 9.20v 6.3v 10 5 11.6v 7.0v 12 6 13.8v 9.0v max charging current is 1/4 of the battery's capacity charging time is 1.4x the the capacity @1a stop charging if the current is less than 45ma(battery is charged) stop if battery gets hot.


approximate numbers: a 12 volt sla has 9 cells and is charged at 14.5, and dead at 11.5 each cell is charged at 1.61 volts and dead at 1.27 a 4 volt sla likely has 3 cells in it charged full 4.83v, at dead at 3.8v Apply 4.8 volts, and monitor current flow. When current stops or slows down, its charged. 4.5 amp hours capacity will charge at 1 amp for about 5 hours, or 5 amps for about 1 hour.

You win the prize for not reading the rest of the thread.

Where did you get those numbers? Lead-acid cells are 2V. 6V batteries have three cells, 12V batteries have six. A 4V SLA should have two.

I guess I should have wikipedia'd it:

"Each cell provides 2.1 volts for a total of 12.6 volt at full charge"

I was stuck on the long ago memory that its hard for a standard electro-chemical reaction to exceed a voltage potential of 1.5 volts. I guess that's why lead acid has been so popular for a century.


I stand corrected! Use Cameron's numbers!

You know the important bit that is the rated voltage 4v the battery impedance will take care of your current draw. I would look for a wall wort (the little black ac to dc converter that comes with most every answering machine or small appliances) rated at 6vdc. make sure all the pluses and minuses line up and your good to go. hook up your volt meter across the power terminals and watch it charge. I wouldn't leave it for days three hours should do it. I'll admit it's not real sexy but for this simple is better. cheers