VRLA 12V Voltage Range?

[FoxMeister88]

I pulled 4 VRLA 12v batteries from a UPS unit and I can't seem to understand the datasheet and what the voltage range is. What I am trying to accomplish is do a capacity test but I do not have a BMS on hand, so the idea is to first charge them manually with a variable power supply and then do the cap test.

The datasheet shows ranges of 1.30v to 1.80v... but it's a 12v battery.

 

[snoobler]

I pulled 4 VRLA 12v batteries from a UPS unit and I can't seem to understand the datasheet and what the voltage range is. What I am trying to accomplish is do a capacity test but I do not have a BMS on hand, so the idea is to first charge them manually with a variable power supply and then do the cap test.

The datasheet shows ranges of 1.30v to 1.80v... but it's a 12v battery.

12V lead acid AGM do not use a BMS, so you do not need one.

Nominal capacity, 10hr: 8.0Ah, i.e., this battery can deliver 0.8A for 10 hours.
Max charge rate: 2.4A.

The chart clearly indicates V/cell, so you multiply those numbers by 6. They represent the END of the discharge. Example:

You take a fully charged battery, apply a 66.2W load OR a 5.52A load current. This will deplete the battery in one hour (60 minute column) and terminate at 1.8V*6 = 10.8V. It permits deeper discharges, but as you can see, the gains in discharging lower are negligible.

Given that they are designed for UPS units, they are designed for higher discharge currents (120A) and slow charge currents. They are also not deep cycle batteries. They are designed for high power for short periods of time. They are a very poor choice for a cyclic power system such as off grid solar, etc.

I don't see any charge voltages. If they are not on the battery, I would charge as follows:

Use an adjustable power supply.
Set voltage to 13.8V and current to 0.
Attach battery
Increase current to 2.4A
Leave on charger for 24 hours.

You could do all 4 at once by putting them in parallel and setting the current to 9.6A.

 

[FoxMeister88]

Perfect, thank you. I was looking online and got so many different answers and voltages I wasn't sure what to believe.

Thanks for the clarification!

 

[snoobler]

13.8V is essentially THE charge/float voltage for AGM batteries in a UPS application.

Many AGM batteries will list two performance categories:
1) cyclic (off-grid storage, daily cycling) where there's an absorption voltage of 14.X and a float of 13.2-13.8.
2) standby (UPS, infrequent cycling) - almost always 13.8V.

The 24 hours is a guess on my part to ensure you get the last little bit of juice into them.

You could also likely charge them via a standard 14.4V absorption with 13.2V float, BUT that's much more of a guess on my part. Pretty confident if you treat it as though it was in its intended application, it will give the best results for comparison to their ratings.