I use two of these, one for each direction of current. The wiring diagram included shows how to hook up both and only uses one shunt to do it, you will wind up with a spare shunt. They have been in place for about 3 years. The 100 amp limit is not an issue for us we use a small 300 watt inverter for ant A/C loads that we may need and do not have the capacity to connect the house battery to engage the engine starter. There were no issues with starting the Onan.
A much better way than using battery voltage alone to ascertain state of charge. If you look at a temperature dependent state of charge chart for lead acid batteries there is quite a difference between 30* and 100* as far as battery condition/voltage are concerned. Chart:
The colors in the chart coincide nicely with postings from Booster that show the fallacy of worrying about ruining a battery if you take it below 50%, instantly showing when you should be cognizant of state of charge indicated by the yellow area on the chart. I have a copy of the chart posted on the inside of a closet door. Quite convenient given that the areas we camp in range from 30* to about 110. Another good reason to have a solar/charging controller with temperature compensation, you have an instant read out of the actual battery temp, at least with the Renogy solar controller that we employ. Our converter, PD4645, does not use temp conversion.
You will notice drift in the amount of spread between out going and inbound "total watt hours" as there is no feature to compensate for charging losses. Simple enough to do, though you have to use a tooth pick or similar to access the recessed operation button. A bit of a pain, but minor.
These work very well to monitor the battery and the solar system. The one thing that would be nice to have different would be for the total current to be in amp hours instead of watt hours.
I would buy them again. Not an elegant solution but still workable. And definitely frugal. A note specifically for persons familiar with the motorcycling world: yes, I own a KLR650.