AGM Battery Resting Voltage
Last year I purchased a set of 4 Rolls S12-230AGM-RE batteries. They've been installed since October and working great since then. I don't have a problem but instead I'm observing something that doesn't seem normal (at least in my experience).
For the past month, the batteries have been "at rest" meaning there is no charge or discharge on them. Also for the past month, I've noticed that their total voltage has remained at "52.0V" all that time. I think I was expecting them to rest at about 50V, maybe a bit higher. Converting to a per-unit measurement they average: 52/4 = 13.0V each. Is this normal for an AGM battery?
Ruling things out: The two different sources that could recharge these batteries (an inverter and a wind turbine) have been disconnected at the breaker and shut down, respectively. There haven't been any unusually hot or cold temperatures here (Calgary). The batteries power a little LCD voltage meter that's been displaying "52.0" plus or minus 0.1 all this time, but that's a phantom load, not something that would supply a charge.
I've consulted some data for these AGM's on the Rolls website's support pages. I found a chart of open-circuit voltage versus SOC which suggests that 100% SOC has a resting voltage of 12.8 to 12.9V, which is getting close to what I see. But that's for 25degrees C, and these batteries live at ambient temperature, which is more like 0 - 10 degrees C in the spring. I should add that I don't think these batteries really were at 100% SOC when they were disconnected. In early April, the temperature would have been about 5 degrees C, meaning the maximum SOC would have been about 90%. If I made a prediction based on this information, I would expect 12.6V * 4 = 50.4V today. The same charts show that self-discharge isn't a factor at these temperatures (which is great).
Does anyone see anything unusual about 52.0V?
(or 13.0V per battery, I should say?)
Topic: AGM Battery Resting Voltage (Read 58 times)
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