The instrument is accurate. Whether the number on it is true depends entirely on what happened at installation.
Put the shunt where nothing bypasses it
Every cable that used to reach the battery negative moves to the load side of the shunt: loads, the solar controller, the DC-DC charger, the mains charger, the chassis bond on a vehicle. The battery is the only thing on the other side. One forgotten connection makes its current invisible, and the resulting error never corrects itself.
Enter the bank you actually have
Capacity, chemistry and charge efficiency, taken from the battery in front of you rather than left at whatever the monitor shipped with. A percentage derived from another battery is internally consistent and unrelated to anything.
Set the full-charge criteria so they can be met
The monitor decides a charge is complete from a voltage, a tail current and a duration held together. Set unrealistically, none of them is ever reached, the monitor never re-synchronises, and it drifts indefinitely. Set them against what the charging sources genuinely achieve.
Prove it before trusting it
Clamp meter against the monitor under a known load: they should agree. Then charge fully and watch for the monitor to detect it. Two checks, ten minutes, and the difference between a reading and a guess.
Write down what was entered
The settings, the shunt rating and the date. In two years, when the percentage looks wrong, that note is what separates a configuration question from a battery question.
What people ask before they order
Can I check it without special equipment?
A clamp meter on the main negative, compared with the monitor at the same instant, answers the wiring question in one measurement. Agreement means everything is passing through the shunt.
Why does it drift even when wired correctly?
Because counting accumulates small errors and the monitor resets against a detected full charge. A system that never reaches its full-charge criteria never resets, and the error grows in one direction.
Last reviewed 16 September 2026