Victron BMV-712 Smart

This is the BMV-712 Smart battery monitor: a round head unit with a display and Bluetooth, supplied with the 500 A / 50 mV shunt, a 10 m RJ12 cable and a 2 m battery-positive lead carrying a 1 A slow-blow fuse. The datasheet gives a 6.5–70 V supply range, under 1 mA draw with the backlight off, a VE.Direct port, a 60 V / 1 A bistable relay and an auxiliary input for a second battery's voltage, a temperature sensor or a midpoint. The head is IP55 and not meant for outdoor mounting. Its sibling, the SmartShunt, is the same shunt without the head.

The shunt goes in the battery negative, and the rule that makes the monitor right is simple: the battery's negative post connects to the shunt's battery side and to nothing else, and every load, charger, inverter and chassis ground lands on the other side. In Crimp those two studs are BATT − and LOAD −. The fused red lead from the shunt's circuit board goes to battery positive and is B+ sense on the canvas; AUX sense is the auxiliary input. The RJ12 cable to the head carries data only. Victron's installation section has the connection diagrams.

The technical reference above sizes the example battery-negative run with Crimp's engine from the connected loads and chargers, not from the shunt's 500 A measuring range. Cables to the shunt's M10 bolts follow the system, not the shunt.

• State of charge is calculated, not measured. It counts amp-hours through the shunt and resets to 100 % only when three conditions hold at once: charged voltage, tail current and a charge-detection time. The defaults suit lead-acid; set them for your battery and set the capacity, Peukert exponent and charge-efficiency factor, or the reading drifts. The manual's troubleshooting section walks through it.
• The aux input does one job at a time. Second-battery voltage, temperature or midpoint, never two together, and the temperature sensor (ASS000100000) is a separate purchase. Choosing starter-battery voltage means giving up temperature compensation from this unit.
• Anything on the battery side of the shunt is invisible. A charger or ground strap landed on the battery post instead of the load side is counted wrong or not at all. Only one cable belongs on the battery post.
• A monitor draws current too. The datasheet's own warning: a lithium battery discharged to its low-voltage cut-off has almost nothing left, and a residual draw of 10 mA can damage a 200 Ah battery left in that state for a little over a week. Disconnect or keep charged during storage.
• The relay is small. 60 V / 1 A, bistable, invertible; it drives a contactor or a signal input, not a load.

• Most "wrong reading" threads are shunt wiring. Something else on the battery side of the shunt, or a return that bypasses it, shows up as a monitor that never agrees with the charger; see this Victron Community thread, the Escape owners' corrected wiring and a DIY Solar Forum case. Charge showing as discharge means the two heavy cables are swapped, per the Ford Transit forum.
• "It never reaches 100 %" or "it jumps to 100 % too early" are settings. Owners resolve it by raising the charged voltage for lithium, setting the tail current just above the charger's, and adjusting Peukert and charge efficiency; see this thread, this one on the efficiency factor and the DIY Solar Forum.
• BMV-712 or SmartShunt is the pre-purchase question. The consensus is that both report the same data to VictronConnect and a GX device, and the BMV adds the display, the alarm and the relay, with better Bluetooth range because the antenna sits in the head rather than in the battery box; see this comparison thread, YBW and the Footprint Hero review.
• People want the aux input to do two things. Threads asking to monitor the starter battery and the temperature at once end with "one or the other"; see this one and this one.

• The SmartShunt 500A page covers the same shunt without a display, including where it sits next to a Lynx Distributor.
• A monitor is how you see what a DC-DC charger delivers: pair it with the Orion-Tr Smart 12/12-30 or Orion XS 12/12-50A.
• Size the battery-negative run with the wire size calculator, and use the fuse checker for the battery-positive protection the monitor's lead does not provide.
• Open a complete boat starter/house example or a campervan system; each opens in Crimp.