I've had the link 10, Link 20 & Victron battery monitors, liked them all and agree with Greg that every cruising boat should have them. The Victron is by far the easiest to install. They have a small circuit board on the shunt and the wiring is simply to connect the battery positive to the circuit board on the shunt, then something that resembles a phone cable with those snap in connectors (RJ11 connectors) connects the shunt to the back of the monitor.

I liked the Victron, but it failed after I took on water while the engine was running. The water got high enough to reach the bottom of the fly wheel before it was detected and was sprayed around the engine room. This caused a number of problems eventually, and one of them was that the circuit board on the shunt (which was located in the engine room) basically dissolved with corrosion. Once back in the US, I ordered a new shunt, but as the old one was dying, it apparently also took out the battery monitor.

I've chosen to replace it with the Clipper unit (ordered but not yet arrived) for two reasons.

1) It uses the standard dumb shunt which should be able to survive being sprayed with salt water.

2) It's display shows both the current voltage and amperage in/out of the batteries as well as a state of charge (SOC) indication without having to press any buttons. By the way, I fully agree with the other comments regarding the SOC usefulness. In my experience, what I really want to see is the current voltage and amperage. After living aboard for awhile, you get to know what these should be under various conditions and develop a feel for the relationship between them. When I first started cruising, I basically destroyed a set of batteries from blindly believing the SOC indication and not checking the voltage. (We were 3 days out of the Galapagos on our way to the Marquesas at the time, but that's another story for another time and place.)

The only down side of the Clipper unit for me is the physical size of the display. I would prefer it to be smaller. I'm going to have to rework the panel a bit when I install it.

p.s. I have since installed a bilge water alarm.