I bought a SmartShunt 500, used, a few weeks ago and installed it last week. I tested it for about a minute with a plain lead-acid battery at the time of purchase, and it showed the expected voltage then (measured with known-good multimeter at the same time). After installing it in my boat, a simple 12 V system, it initially showed normal and reasonable voltages. But by the next morning, voltage was already up at almost 15 V, and it kept on climbing. By day two, it showed over 21 V, and later that day reached close to 27 V.
I completely disconnected the small solar panel (connected via a Victron PWM regulator) the second day, which changed nothing. All these readings were with the engine off (it's a sailboat) and with no shore power connected. So, the only source was the bank of lead-acid batteries, all at ~12.8 V, measured using two different Raymarine plotters, one analog volt meter on the instrument panel, and two different multimeters, all agreeing to within ~0.2 V or so. I measured with the multimeters across the battery minus connection on the shunt and the thin positive lead connected to the VBatt+ port on the SmartShunt, so exactly what the SmartShunt should be seeing.
Latest versions of the firmware available installed, according to the app.
I've tried leaving it unpowered for several minutes, to see if that reset it, but nothing changed. I've reset to defaults in the settings, but that obviously did nothing to the voltage reading.
The last thing I tried before I had to leave the boat was to remove it from the electrical system of the boat, and connecting it straight to a completely separate 12 V lead-acid battery. No other connections from the shunt or the battery. It still showed ~26 V.
The only thing I haven't tried is to switch it over to DC Meter mode, and back again. I don't have much faith in that helping, but it seems to me to be the only thing left to try, unless someone suggests otherwise here.
The boat, and the SmartShunt I forgot to bring with me from the boat, are unfortunately 2.5 hours away by car, so I won't be able to try new things with it until maybe Friday or Saturday.
Since I bought it used, I can't return it to a store, or make a warranty claim. My only hope is that someone here knows what the issue is and that it can be fixed. If not, well, I'll just have to accept that I bought a would-be dud.
