What is Parasitic Draw and How Does it Affect Commercial Vehicle Batteries?
Parasitic draw is the small but continuous amount of electrical power consumed by equipment when a vehicle or piece of transport equipment is switched off or not in active use.
On modern commercial vehicles, there can be numerous systems drawing power from the battery in the background. Individually these loads may be relatively small, but over time their combined effect can significantly reduce battery state of charge – particularly when a vehicle is parked for extended periods or operates on a low-mileage duty cycle.
What Causes Parasitic Draw on Commercial Vehicles?
The source of parasitic draw varies depending on the vehicle and application.
Telematics, tracking equipment, monitoring systems, cameras, alarms and other connected technology can all require power while a vehicle is stationary.
In refrigerated transport, for example, telematics, temperature monitoring and fridge controllers can create an ongoing electrical demand on the refrigeration unit battery.
Electric light commercial vehicles (eLCVs) present a different example. Despite having a large high-voltage traction battery, they still rely on a conventional 12V auxiliary battery to operate many critical vehicle systems. Ongoing electrical loads can contribute to discharge of this battery, potentially leaving the vehicle inoperable even when the traction battery has sufficient charge.
As commercial vehicles become increasingly connected and reliant on electronic systems, managing these background electrical loads is becoming increasingly important.
Why Does Parasitic Draw Cause Battery Problems?
A healthy battery can accommodate small electrical loads for a period of time, but problems can arise when the energy being taken from the battery isn’t sufficiently replenished.
This is particularly relevant for vehicles and equipment that spend long periods stationary, operate infrequently or complete short journeys that provide limited opportunity for the alternator or vehicle charging system to restore the battery.
Repeated periods at a low state of charge can contribute to premature battery degradation as well as increasing the risk of a flat battery and associated vehicle downtime.
How Can Solar Help Offset Parasitic Draw?
Vehicle-Integrated Photovoltaics (VIPV) can provide a simple way of replenishing some of the energy being continuously drawn from the battery.
A solar battery-maintenance system harvests available daylight and provides a controlled charge to the vehicle or equipment battery. Rather than allowing background electrical loads to continually deplete the battery while the vehicle is stationary, solar provides an ongoing source of energy to help offset that demand.
This doesn’t mean the solar panel needs to power all of the vehicle’s electrical equipment. In a battery-maintenance application, relatively small amounts of energy delivered over time can make a significant difference to battery state of charge.
The result can be improved battery health, fewer flat-battery incidents, reduced battery-related downtime and potentially longer battery life.
Parasitic Draw Isn’t Just a Refrigeration Issue
Our earliest solar battery-maintenance applications addressed parasitic draw in refrigerated transport, but the same principle now applies across a much wider range of commercial vehicles.
Read our in-depth guide to understanding parasitic draw in transport refrigeration.
Whether the electrical demand comes from refrigeration monitoring equipment, telematics, connected vehicle technology or the critical systems operating from an eLCV’s 12V battery, the principle is the same: if energy is continually being taken from a battery, it needs to be replenished.
Solar provides a way of doing that whenever sufficient daylight is available, without relying solely on the vehicle being driven or the engine being run.
