The basics of battery monitoring

There is a never-ending list of gadgets available for 4x4s and recreational vehicles that become more a question of priority (which should I do first?) rather than one of necessity (do I need it at all?). Dual battery systems, for most people, definitely land on the required and high priority list. Depending on the use of the system it can really just be set and forget – such as the weekend warrior just hoping to run a fridge and phone charger on the overnight camping trip every now and then.


Ensure optimal performance of your auxiliary battery 

More demanding power requirements call for some information about how the system is going during your adventures, to be sure you have power when you need it, plus ensure optimal performance and service life of your auxiliary battery.

This is where the question of “needing it at all” is asked. Some level of battery monitoring can give peace of mind especially when that battery is something that you rely on for safety or necessities. If you know nothing about the battery condition via monitoring, then the only way to find it out is the hard way – when its flat! There are various ways that batteries can be monitored from simplistic voltage and current readings, right through to using these measurements to calculate against battery chemistry and size characteristics.

Solar BlanketSolar Blanket

Voltage measurement is the entry-level battery monitoring solution. Whether a hardwired gauge or wireless solution is employed, it will essentially tell the user the instantaneous voltage of the battery at any given time. Voltage can give you a line in the sand from which you can see if things are behaving as they normally do.

If the voltage is higher than the normal rest voltage observed, then you know the battery is charging. If the voltage is lower than normal rest voltage, it is under load or in a discharged state.


Understand the norm

Learning what is normal for the particular installation is the best way to understand its behaviour and limitations and if everything is ok. As voltage is influenced by charge/discharge and rest periods, seeing something that is abnormal is your indicator that something is going wrong.

There are rules of thumb around battery voltages indicating a state of charge – but better yet the battery data sheet will give more detail. Different battery types, sizes, temperatures, charge and discharge rates will all alter the outcome. Some voltage gauges even feature an alert to let you know when the voltage is not in good shape.

Couple measurements of voltage and current – and now we start to see some more useful information.

Current flowing into or out of the battery will influence its voltage and the amount of current flowing impacts the level of voltage change. The internal resistance of the battery (and dictated by its type and condition) is another of the key factors that determine the voltage change due to this current flow. What this means is that you can have a better understanding of the battery condition given the current flow information.

Helpful fault finding

If the voltage is low despite a very high current flow into it you know the battery is deeply discharged and will take quite some time to charge. If the voltage is high and the current flow into the battery is low you know the battery is nearly full. Faults may be found here, if the battery voltage is high and so is the current flow into it, there may be a battery fault with the battery and the energy could be getting turned into heat. Conversely, if the voltage is low and so is the current flow, there may be a charging system fault, or if charging from solar alone you may just not have enough sun!

All this data about voltage and current can be a bit daunting when you just want a cold beer!


Step up with advanced battery monitoring

Bring on technology to do the hard work! Advanced battery monitoring is often integrated into complete Battery Management System and Total Vehicle Management System as the information used to provide more accurate and meaningful results that are easy to understand starts to involve all aspects of the charger, load, and battery.


Furthermore, higher accuracy current measuring components, that are measuring fractions of an amp right up to hundreds of amps, are used. Shunt type current sensors can provide greater resolution and range than inductive sensors (used in simpler gauges) and are wired in series with the circuit being measured, usually in the battery negative lead. Battery construction and size impact the efficiency of battery charging and effect of discharge currents on the state of charge, all of which can be considered and calculated if you have the information input to the system and monitored in real-time.

To work all that out around the campfire would not appeal to most. Advanced monitors can do all of these calculations and deliver the information in a way that is easy to understand at a glance, similar to what a vehicle trip meter does with fuel consumption “100kms till empty” (under current conditions), monitors can report “5 days till flat” for your dual battery system.


If you want to know more about the batteries in your 4WD take the REDARC virtual product tour to find out what products can help take the guesswork out of your next off-road adventure.