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Discussion Starter · #1 ·
I have some UB12120 12V 12Ah SLA batteries that I want to charge, and I have not found a really accurate specification for the charging specifications. I did find this:

But this information on charging is not quite correct:
Cycle Applications: Limit initial current to 1400mA. Charge until battery voltage (under charge) reaches 14.40 to 14.70 volts at 68º F (20º C). Hold at 14.40 to 14.70 volts until current drops to approximately 3600mA. Battery is fully charged under these conditions, and charger should either be disconnected or switched to "float" voltage.
"Float" or "Stand-by Service": Hold battery across constant voltage source of 13.50 to 13.80 volts continuously. When held at this voltage, the battery will seek its own current level and maintain itself in a fully charged condition.
I think the 3600 mA should be 360 mA. There is also an error on this page for the capacity and current. This battery should provide 7.2 amps for 1 hour (7.2 Ah, Peukert 1.206).

I found some detailed information on flooded lead-acid batteries:

AFAIK, SLA batteries are identical except for the fact that you must limit overcharging that causes gassing, since the vapors released through the vents causes deterioration that can be corrected by adding water to flooded cells.

The label on my batteries is for constant voltage charging and initial current at 20C:

Standby Use 13.6-13.8V 1.2A
Cyclic Use 14,5-14.9V 3.6A

I would like to know the optimum voltages and currents at various temperatures so that I might be able to adjust the parameters for different ambient conditions.

BTW, these batteries can be purchased on eBay for about $20 each, including shipping, with a 10% discount. This makes them about $0.14/Wh at rated discharge, and at 1C (12A) they have 6.5 Ah capacity for an effective cost of $0.26/Wh.

Some other information I found:

I also learned that smaller SLA batteries are AGM construction, while larger sizes may be true Gel Cell types which require different charge profiles.

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There is a charge control IC for sealed lead acid batteries called UC3906.

In the application notes the bulk charge is held at the Overcharge rate until the amps have dropped to 10%. It also compesates for temp.

It will adapt to larger strings of cells and can control a low voltage cut-off.

· Registered
3,143 Posts
Discussion Starter · #3 ·
OK, I appreciate that. I found a link to the app note:

I also found discussions:

And other ICs from TI:

So I guess now I need to incorporate this information into my SLA BMS. Or maybe just get one of these ICs.


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3,143 Posts
Discussion Starter · #5 ·
That's some good information. I took a bit from here and there, and came up with the following specification:

[FONT=Courier New]Initial charge at 0.2C for 5 hour nominal charge time[/FONT]
[FONT=Courier New]12V 12Ah initial charge at 2.4A[/FONT]
[FONT=Courier New]Maintain charging until voltage reaches 2.4-2.5 Vpc = 14.4-15 VDC[/FONT]
[FONT=Courier New]At 14.4V battery is 70-80% charged[/FONT]
[FONT=Courier New]Keep at 14.4 volt until current = 0.02C (240 mA for 12 Ah)[/FONT]
[FONT=Courier New]Float charge at 12.8-13.2V (or initiate new charging cycle at 12.5 volts (90%)[/FONT]
[FONT=Courier New]Voltages are based on 25C. Voltage changes by -0.003 Vpc/DegC. So 14.31V at 30C and 14.49V at 20C[/FONT]
[FONT=Courier New]SOC chart for open circuit voltage after 3 hours rest:[/FONT]
[FONT=Courier New]SOC   Vpc    V12[/FONT]
[FONT=Courier New]100%  2.116  12.700[/FONT]
[FONT=Courier New]90%   2.083  12.500[/FONT]
[FONT=Courier New]80%   2.070  12.420[/FONT]
[FONT=Courier New]70%   2.053  12.320[/FONT]
[FONT=Courier New]60%   2.033  12.200[/FONT]
[FONT=Courier New]50%   2.010  12.060[/FONT]
[FONT=Courier New]40%   1.983  11.900[/FONT]
[FONT=Courier New]30%   1.958  11.750[/FONT]
[FONT=Courier New]20%   1.930  11.580[/FONT]
[FONT=Courier New]10%   1.890  11.340[/FONT]
[FONT=Courier New]0%    1.750  10.500[/FONT]
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