This is the gauge part of the Victron BMV-602S battery monitor. It "wires in" with a simple click of a Cat-5 type cable end. I was installing this "on the road," without access to a lot of tools, and there was a left over hole here from where the Wallas control used to be. So I decided to put it here initially and see how I liked it. I just bought a blank outlet cover from a hardware store and cut it to fit the gauge. This allowed me to make the best use of the existing hole.

Now that I have used it for awhile, I think I would like to have it at the helm, so I can also easily view it underway, so it's on my to-do list when I next have access to tools/vacuum/etc.