Thursday, May 24, 2007 at 07:57
Hi Mike, interesting read and if you carryout similar tests on wet cell batteries, the results are about the same.
I’m with Sand Man on not taking batteries down to 9v.
You can and if you have even the smallest of loads, once the
battery gets to around the 11v mark and this backs what you were saying about how little stored capacity there is bellow 11v, the
battery will get to 9v in a very short time and ANY
battery taken down that low, particularly while under load, will be irrevocably damaged.
When using a fridge with a 10.5 volt cut-out, this cut-out will most likely occur while the fridge is running so that once the cut-out occurs, the
battery’s voltage will actually rise.
There is a complex calculation that gives you the
battery’s capacity using the terminal voltage plus the load being applied to the
battery and based on the size of the
battery, ambient
temperature and so on, that will give you a very accurate indication of the SoC of the
battery and is too make trouble for the average user to both with ( including myself )
As you posted, keeping above 11v is the simplest way to go unless you have something that cuts out automatically for you.
As to AGMs under the bonnet, both Odyssey and Optima make AGM batteries specifically for this use, and I imagine there are others.
Cheers.
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