Monitoring Batteries on Remote, Off-Grid Equipment

On a remote site the battery is usually the single point of failure. If it runs flat, the cameras stop recording, the welfare unit loses lighting and heating controls, the cabinet drops its connection or the pump stops. The first sign is often a phone call from the customer.

Monitoring turns that into a planned decision. If you can see the battery's condition and how quickly it is draining, you can arrange a fuel delivery, a battery swap or a charging fix before the asset stops.

Voltage is easy to measure, but it is a poor guide to remaining energy on its own. It sags under heavy load, rises while charging and shifts with temperature. Lithium batteries in particular hold a very flat voltage across most of their range, so a small voltage change can mean a large change in remaining energy.

State of charge is the percentage of usable energy left. It is worked out by counting the energy going into and out of the battery over time, which is what a battery monitor or a lithium battery's own management system does.

Lithium batteries used on remote equipment normally include a battery management system (BMS). The BMS protects the cells, balances them and can disconnect the battery if it is over-discharged, over-charged or too cold to charge safely. Smart lithium batteries can report state of charge, cell voltages, temperature and alarms over a data connection.

Lead-acid batteries, including AGM and gel types, have no built-in electronics. They are more sensitive to being left partly charged and to deep discharge, both of which shorten their life. Monitoring them relies on an external battery monitor.

A shunt is a precision resistor fitted in the battery's negative cable. Every amp flowing in or out passes through it, so a battery monitor connected to the shunt can count energy accurately and calculate state of charge. It works with lead-acid and lithium batteries alike.

For accurate results, all loads and chargers must connect on the system side of the shunt, and the monitor needs to know the battery's capacity. A device such as the Victron Smart Shunt reports state of charge, voltage, current and estimated time remaining.

Runtime is remaining usable energy divided by the current load. As an illustrative example, a battery with 2 kWh usable remaining and a steady load of 50 W has roughly 40 hours left if nothing is recharging it. In practice, loads vary and charging comes and goes, so runtime estimates should be read as a trend rather than a promise.

Useful low-battery alerts are layered:

In the UK, solar yield in winter can be a small fraction of summer yield, while most remote loads stay constant. Systems that balance comfortably in summer can run a daily deficit from autumn to early spring, drawing down the battery a little more each day.

Watch daily solar yield against daily consumption. When yield consistently falls short, act before the battery does: reduce overnight loads, check panels for dirt and shading, confirm backup generators or fuel cells are ready, or plan more frequent battery swaps for sites without backup.

TrackSyte is an approved Victron integrator. The Neo 2 gateway connects to Victron equipment, smart lithium BMS batteries and the Victron Smart Shunt, and adds cellular connectivity and GPS. The TrackSyte Portal then shows state of charge, battery voltage, current and power, estimated runtime, solar yield, loads, inverter and charger status and alarms for each asset, with alert rules and notifications by email, webhook or Slack.