Lazy Daze Owners' Group

The Balmar SG200 battery monitor does require installation of a shunt. There is an earlier product, Balmar's Smartgauge, that doesn't need a shunt. I installed one of these in my Lazy Daze, and it worked pretty well. But I also had a Victron BMV series shunt-based battery monitor that gave me information about moment-by-moment charging and power consumption--information that the Smartgauge was not able to supply.

The SG200 is a much more advanced product that combines shunt-based current measurement with algorithmic monitoring of batteries' state of charge and state of health--the latter a unique capability, as far as I know. Given that the costs of these two units are within a few dollars of each other (about $230), I'd say if you can possibly find space for the SG200's shunt, it will give you more and better information for your money.

"In one of the reviews for this a user didn't like the app interface. They claimed this one is much better."

From the screenshots I've seen, the Thornwave software looks fine*. But I don't have a problem with the VictronConnect app's interface. It's one of the best I've seen, and I speak both as a former software designer and as a user who's easily irritated by awkward software. It has the added advantage that it works equally well with all of Victron's "Smart" devices, from shunts to battery monitors to solar charging controllers to battery chargers to inverters and beyond. The Victron app is frequently updated--not just left to age out, as is the case with some hardware-support apps I've seen. (I'm not saying Thornwave is guilty of this, because I don't know; just that Victron definitely isn't.)

But there's a more important point to be made here. In my reply #2 in this thread, I explained why no battery monitor that is purely shunt-based--Victron's, Thornwave's, Bogart's, or others--can be trusted in the long run, because all of them slowly drift out of calibration as batteries lose capacity over time. They can be manually recalibrated, but doing so is pure guesswork (the "10% a year" rule of thumb) unless you have the equipment to load-test your batteries. That's time-consuming and generally a pain. I've tried it. I know.

Because the Balmar SG200 uses not only a shunt but a microcomputer that monitors battery status hundreds of times a second, and evaluates that using an algorithm that Balmar has developed over more than a decade of experience with all types of batteries, it's not only able to give accurate readings of battery state of charge (including for lithium batteries) and current flow in/out, but also to continuously self-recalibrate as the batteries lose capacity over the years, and in addition, to give a continuously updated readout of battery state of health. That last is something no purely shunt-based monitor can do.

So here are your best choices, in my humble opinion. If you can live without a display and are content with doing guesswork recalibration every year or so, Victron's SmartShunt is a good value for $130. If you want a display, you could buy Victron's well-known BMV-712, which was the standard recommendation for a lot of us for a good many years, for $206. Both have Bluetooth built in, so they'll work with the Victron app on phones, tablets, or desktop computers. But both are purely shunt-based, with the drawbacks I just mentioned.

For $230 you can get Balmar’s SG200, which has major advantages over the shunt-based  monitors... and, by the way, a much nicer display than the BMV-712. But to make it an apples-to-apples comparison, if you want to be able to monitor status remotely, you'll need to add the SG2-0300 Bluetooth Gateway, a $59 dongle that lets you use Balmar's app. (Balmar really ought to be building in the Bluetooth capability, to stay competitive.)

As for the Thornwave product, I don't see any advantage to it. By the time you add a good shunt, it'll cost you close to $200, while doing the same jobs as a $130 Victron SmartShunt. The SmartShunt has the added advantage of being a one-piece solution.

I went the SG200 + Bluetooth dongle route, because I'm delighted not to have to find a place to mount yet another display and run wiring to it. I'm happy checking my battery status on my iPhone.

* By the way, all the screenshots of the Thornwave app were taken with the optional-at-extra-cost shunt attached. You won't get all that information with the $130 product as sold.

I want this.
I sent them a message asking when it will be in stock again.

BALMAR SG205

• Two (2) -- 6 inch long, AWG 2 copper battery cables with lugs, one end 5/16", the other 3/8" (sourced from BatteryCablesUSA.com)
• One (1) -- Blue Sea Systems 5/16" PowerPost Cable Connector (sourced from Amazon)
• A small piece of 1/2" plywood used to reinforce the outside of the battery box where the shunt and PowerPost were mounted. Why on the outside of the box? Because there’s so little room inside.