Originally Posted by
Doc_Wui
Again, if the battery shuits off, the wattmeters lose the data. Ive ridden on and on to discharge the battery only to lose the data. They do have connector for an external battery. A 9 V transistor radio (who remembers those) will power it. Then you can let the battery go flat.
I also have a couple of those wattmeters. I was a bit surprised to find that the last one I bought actually retains the data when power is lost. As you suggest, this can be quote useful when doing a capacity discharge test.
Here's the link to the one I bought (the internal shunt version).
DC Combo LCD Panel Meter Car Solar System Battery Voltage Current Power Monitor