I have a battery that came out of service. It was in a UPS. The battery lost its capacity. As soon as power went out the battery was not able to supply the necessary current to keep the computer working. It would drop out in about 15 seconds. I replaced that battery with one just like it but instead of 12V @ 7Ah the SLA I put in its place is 12V @ 9Ah but it's physically the same dimensions and connections.
Here's the weird part: I put the old battery on a 13.8V source (radio shack 13.8V @ 19A power supply). Let it sit for a few days and last check with the PS connected the voltage was 13.6V. That was days ago. I connected an old computer fan to the battery and let it run. It ran over night and the next morning the voltage had dropped to 9.2V. I disconnected the battery and put it back on the PS. Two days ago I disconnected the battery from everything, just let it sit on the bench. For a few days I've been watching its voltage while resting with nothing connected whatsoever. Right now the battery voltage is 13.12. I've checked it with two other meters, and with a few hundredths of a volt have essentially read the same thing. So this battery isn't worth much other than powering small electronics for as yet some undetermined period.
The crux of my question is "Why does a 12V SLA (used) sit at or above 13V?" From all I've ever known about lead acid batteries is that they will rest (new) after charging and then leaving them alone for 12 hours the voltage drops to 12.6V which is normal for a fresh 12V battery. This battery is obviously sulfated on its plates which is why it can't provide any serious current. I'm just curious as heck as to why that voltage is present after two days of rest.
What'cha think?
Here's the weird part: I put the old battery on a 13.8V source (radio shack 13.8V @ 19A power supply). Let it sit for a few days and last check with the PS connected the voltage was 13.6V. That was days ago. I connected an old computer fan to the battery and let it run. It ran over night and the next morning the voltage had dropped to 9.2V. I disconnected the battery and put it back on the PS. Two days ago I disconnected the battery from everything, just let it sit on the bench. For a few days I've been watching its voltage while resting with nothing connected whatsoever. Right now the battery voltage is 13.12. I've checked it with two other meters, and with a few hundredths of a volt have essentially read the same thing. So this battery isn't worth much other than powering small electronics for as yet some undetermined period.
The crux of my question is "Why does a 12V SLA (used) sit at or above 13V?" From all I've ever known about lead acid batteries is that they will rest (new) after charging and then leaving them alone for 12 hours the voltage drops to 12.6V which is normal for a fresh 12V battery. This battery is obviously sulfated on its plates which is why it can't provide any serious current. I'm just curious as heck as to why that voltage is present after two days of rest.
What'cha think?