Monitor basics
Battery Monitors & Shunts Explained
A battery monitor is the fuel gauge for your off-grid system. It tells you how full your bank really is, how fast you are draining it, and how long you have left. With LiFePO4 it stops being a nice-to-have, because the voltage stays nearly flat from full to empty, so a voltmeter cannot read the charge level. The fix is a shunt, and this guide explains how it works and which monitors are worth buying.
How to choose
How to pick a battery monitor
Use a shunt, not a voltmeter
LiFePO4 voltage stays nearly flat from full to empty, so a voltage reading cannot tell you the charge level. A shunt counts amps in and out and always knows the real state of charge.
Size the shunt to your current
A 500A shunt covers most 12V vans and RVs. A large 48V bank with a big inverter is happier on 1000A. Sizing up never hurts accuracy.
Decide on a screen or your phone
The Victron SmartShunt uses the VictronConnect app over Bluetooth. The BMV-712, Renogy, and AiLi add a physical display you can glance at.
A monitor is not a BMS
The monitor only watches and reports. The protection job, cutting off charge or discharge in a fault, belongs to the battery's BMS. You want both.
Roundups and references
Find the right monitor for your build
Best Battery Monitors for Off-Grid
The top shunts and monitors compared, from Victron to budget coulomb counters.
Best 12V LiFePO4 Batteries
The lithium banks these monitors are built to watch.
LiFePO4 Voltage Chart
See exactly why the flat voltage curve makes a shunt essential.
Best MPPT Charge Controllers
The other half of a clean LiFePO4 charging setup.
Frequently Asked Questions
Why do I need a battery monitor for LiFePO4?
Because LiFePO4 holds a nearly flat voltage across most of its charge, a voltmeter cannot tell you whether the bank is at 80 percent or 30 percent. A shunt monitor counts every amp in and out, so it always knows the true state of charge. It is the only reliable fuel gauge for a lithium bank.
What does a shunt actually do?
A shunt is a precise low-value resistor that all of your battery current passes through. The monitor reads the tiny voltage drop across it to measure exactly how many amps are flowing, then adds it up over time to track how much energy you have used and how much is left. It installs on the negative side of the battery.
Which battery monitor is best for most people?
The Victron SmartShunt 500A is the common pick. It is accurate, has Bluetooth, and uses your phone as the display. If you want a wall-mounted screen, the Victron BMV-712 adds one. Our roundup compares them and the budget options side by side.