I've been using this device for several months of continuous cruising now.
I am still convinced that amp-counting battery
monitors are practically useless (I removed, then finally sold my Victron one). That's not to say that they are not capable of giving any useful information at all, but by the time you keep them in proper calibration and interpret them properly you will have expended a lot more effort to get a lot less precise information, than you can get by other means.
The SmartGauge is widely praised as a superior approach to battery
monitoring, and is used by military and commercial
operations, has been thoroughly tested by different people including our own MaineSail, all with the results that this device gives a much better picture of the state of your batteries.
This all may be true, HOWEVER -- my experience has been that I am getting practically zero information from the SmartGauge, which I was not getting from simply monitoring system voltage and referring to a simple table taken from the Trojan Batteries site.
I used system voltage plus the table for several years, and checked the accuracy several times by taking specific gravity measurements.
My method for using system voltage is very simple -- you don't try to do Open Circuit Voltage, after resting the batteries for 12 hours etc., which is the technically correct way to do it. That's because this is completely impractical on a cruising boat which is in actual use. What I do is to read system voltage when there are no big loads on, and no charging
has taken place for some time. The idea is that small loads will not pull down the voltage that much, AND any error will understate the battery state of charge, which is a harmless error. I decided that this would work ok because I don't actually need more precision than 10% or so.
Specific gravity tests showed that the method is actually far more accurate than that -- more like 2% or 3%.
I was delighted with this, as it was far simpler than interpreting an amp-counting meter, and required nothing more than a cheap
voltmeter (but carefully wired directly to the batts with large cross section cables).
The only problem was that this method cannot tell you how much charging
you have accomplished, during a charging run. If you charge for a while on generator
and stop before the charger
goes into float mode, you just don't know how far you got until some hours later when the surface charge is off the batts.
So I thought the Smart Gauge might be the answer to this. I bought one last year and finally got around to installing it over the winter.
Well, the Smart Gauge is not an answer to this. It does attempt to estimate how far you have gotten during a partial charging run, but it is wildly inaccurate. It settles down and gives you a true reading only -- hah, after several hours, after the surface charge is off the batts.
So in summary -- it's a good device, undoubtedly more useful and far more accurate than amp-counting gauges, but I have not discovered any way in which it is significantly better than simply monitoring system voltage.
Now I am sure that this can be overcome with further development. Voltage rises throughout the
bulk phase. This must correspond to state of charge achieved. A really accurate picture could surely be achieved by mapping charging current
vs voltage -- no? Then the device could time the absorption phase and estimate the state of charge achieved per minute of absorption charging by "learning". So maybe SmartGauge v2.0 could have a Hall-effect ammeter to measure charging current
, and could use this data to calculate state of charge achieved during charging.
Of course it may be that we don't actually need that much information. The main thing we need to know is when to charge. We probably don't need to know that with very great accuracy. But we would not want an error on the wrong side -- where we have an exaggerated idea of the state of charge of the batts, so we charge too late, because we were not informed about how deeply discharged the batts had become.
So for this, actually, simple voltage monitoring fits the bill exactly. The state of charge can be understated if you read the voltage with too much load on, but CANNOT be exaggerated. And it's actually remarkably accurate, about 2% to 3% according to my tests.
I still have my old table from Trojan, on my instrument panel. It's amusing to see that the battery state of charge read from this table, always corresponds EXACTLY to what the SmartGauge is telling me.