A battery monitor is the difference between guessing your state of charge and actually knowing it. The Victron SmartShunt (~$120) is the most common choice for US van and RV builds — here's how it goes in.
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Why voltage alone isn't enough for LiFePO4
A lead-acid battery's voltage drops fairly steadily as it discharges, so voltage is a rough proxy for state of charge. LiFePO4's voltage stays nearly flat across most of its usable range — a battery at 90% and a battery at 30% can read almost the same voltage. A shunt-based monitor instead measures the actual current flowing in and out and integrates it over time, giving a real percentage.
Where the shunt goes
The SmartShunt installs in the negative cable, between the battery's negative terminal and the system's negative bus bar:
Battery (-) → SmartShunt → Negative bus bar → all loads & charge sources
Every circuit's negative connection must route through the bus bar on the shunt's "load" side — if any circuit's negative bypasses the shunt directly to the battery, the monitor won't see that current and its readings will drift.
Don't run any negative wire directly to the battery post
Once the shunt is installed, the battery's negative post should only connect to the shunt itself (and the chassis ground bond, on the shunt's battery side). Everything else routes through the negative bus bar on the other side of the shunt.
Configuring for LiFePO4
The SmartShunt ships with lead-acid defaults. In the VictronConnect app (Bluetooth, free):
- Set battery capacity in Ah to match your battery.
- Select or create a LiFePO4 battery profile — set the charged voltage and "tail current" (the current at which the battery is considered full) per your battery's datasheet.
- Set the discharge floor to match your battery's recommended minimum (often around 10-20% for longevity, even though LiFePO4 can go lower).
Getting these values from your specific battery's manual matters — generic lithium settings can cause the percentage to drift over time and need periodic resyncing.
What it tells you
- State of charge (%) — the headline number
- Current (A) — positive when charging, negative when discharging, from every source/load combined
- Time remaining — an estimate based on current draw
- Consumed Ah and historical data — useful for diagnosing whether your charging matches your usage
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