Van Gogh and my kid's artwork are both paintings, it's those "extra little magic details" that make the results so very different.
If a voltmeter's all you want, can get a collection of dozens for that price, why waste your $30 on all that unit's bells and whistles?
Both the device that I posted about above, and the SmartGauge use voltage as the only inputs to determine State Of Charge. SmartGauge has some special-proprietary-seceret sauce that makes it, and it alone, better?
Minne's and my experience with the SmartGauge show that we are not true connoisseurs of SOC gauges. In my case, I have become skeptical of the device. Several other posters here that have experience with the device seem to be of like mindset.
I will conceed that the SmartGauge has provisions for alternate battery chemistries, but the question raised by Minne in this thread is how accurate the magic inside the SmartGauge is at translating from the voltage input into SOC. After having a SmartGauge on my boat for the past five years I now have my doubts as well. In my experience the SOC seems to drop precipitously from the mid-90s to the mid-70s when I have applied little to no load (keeping my cellphone above 80% charge and powering an LED pilot light for about 2 hours) on my 220AH House bank.
For reference- my SmartGauge was installed with AWG 14 wire, and uses an ATC 3A fuse on each lead to the battery bank's positive lead. There are no shunts or inverters in my electrical system, and my boat spends most of the time in the summer on a mooring.
The BlueTooth device above graphs voltage over time which is something that the SmartGauge does not do. If I am understanding the directions, this doo-hickey also records up to 35 DAYS of information at 10mS intervals AND it makes this information available via BlueTooth, which means that I don't have to stop whatever it is that I am doing at any given time to push a button on the SmartGauge or mess with the probes on any of the several DVMs that I keep aboard.
The ability to graph battery voltage over time at the sampling interval will allow me to analyze; how powering my cellphone and the pilot light are really affecting the battery voltage over time, how running my 12VDC refrigeration impacts my battery bank voltage - that is when I choose to run it, how *exactly* my alternator's output (Leece-Neville 90A) affects my battery, and what happens to my battery when I am at anchor.
Your comment about my "wasting $30 on this unit's bells and whistles" makes me suspicious. What is YOUR connection in Balmar or SmartGauge? My relation to SG is that I am a customer, and I have helped sell a couple of them to my clients. Before I decided to purchase my SmartGauge I spent several hours reading everything at their UK website: SmartGauge Electronics - SmartGauge battery monitor
My experience is this: after I spent/invested/wasted $331 for a SmartGauge in April of 2014, I have never feelt "warm and fuzzy" about the SOC that the SG tells me that I have in my battery bank. I believe that the <$32 spend/investment/waste to record and analyze battery voltage history
with this device is worth it to me. YMMV.