In my box of bits, I've got a Lascar DPM400 (http://www.lascarelectronics.com/pdf-usb-datalogging/data-logger0602353001277710769.pdf) voltmeter. This looks ideal for attaching to my leisure battery box that will be running my electric fence next year (starting tomorrow!)
However, I'm not sure how to connect it. I think I need to follow the supply voltage example in the datasheet but do I use the battery positive for the V+ and the negative for the V-, or should the negative be connected to COM? If not, is COM just left floating?