12v systems in a car, van or 4×4 are a huge part of camping. They allow us to run 12v accessories like portable fridges, air compressors and LED camping lights. They can also get incredibly complicated, incredibly fast! If you’ve ever been a little confused by just how much charge your battery has left in it, you’re not alone. It sometimes seems like you need to be an electrical engineer to understand battery voltage! However, if you break it down it’s actually a little easier to understand than it seems at first glance, and all you need is a very basic $10 multimeter to help you understand what’s happening.

The Adventure Kings deep cycle AGM batteries are built for 4WDing. They’re tough, have a large reserve capacity so they can power accessories like a portable fridge for a long time off a single charge and the Absorbed Glass Matt technology means you can run them safely inside a vehicle. Using your multimeter or a volt meter wired to the deep cycle battery is how you can read what your 4WD battery is doing in terms of charging and discharging, and while it isn’t an exact science, it will give you a rough idea of how much power is left. Here’s our guide to understanding the basics of battery voltage.

BATTERY VOLTAGE AT REST

A healthy deep cycle battery that has been sitting for at least 15 minutes and has no load on it (i.e. nothing being powered off it) should have a battery voltage that reads somewhere between 12.6v and 13.1v. If it’s anything less than 12.6v and there’s absolutely, definitely nothing being powered off the battery, it’s a good indication that the battery isn’t in the healthiest condition. That most likely means it’s time to replace the battery, so make sure you check out the Adventure Kings range of AGM deep cycle batteries before you shop anywhere else!

BATTERY VOLTAGE WHILE CHARGING/ENGINE RUNNING

Here’s where it gets a little tricky. Traditionally, a battery that is being charged by the vehicle’s alternator should read somewhere between 14.0v and 14.4v. However, modern vehicles equipped with ‘smart’ alternators don’t always put out a full charging output in an effort to reduce load on engine and emissions. Sometimes you’ll see as little as 13.0v-13.2v coming from your alternator, which often isn’t enough for a dual battery system like the Adventure Kings Smart Isolator Dual Battery Kit to realise that the motor is actually running and connect the auxiliary battery to the crank battery to charge. That’s why a DC/DC charger like the CTEK D250SA is a better option in a modern vehicle with a smart isolator.

BATTERY VOLTAGE WHILE AT CAMP

Okay, so now onto the bit everyone wants to know about. What should a healthy deep cycle battery read at camp, while it’s powering your 12v fridge and LED camp lights? As soon as you introduce any sort of load onto the battery, the voltage is going to drop. With a 12v fridge running and the compressor kicked it, it’s completely normal to see the voltage drop by as much as 0.5v-0.7v. That means you may see your auxiliary deep cycle battery reading somewhere around 12.0v-12.2v while your fridge’s powering away keeping your tucker cold. If you want to properly, genuinely figure out the voltage level of your battery, you need to turn your fridge and LED lights off, and make sure there’s no load on the battery for about 15 minutes before taking a reading. This will allow the deep cycle battery’s voltage to settle so you can get a decent reading.

If the reading is anything under about 11.8v once the battery has settled, it’s time to recharge! That may mean going for a drive, or connecting your solar panel, or even running your generator. Don’t be fooled though into thinking that it’s okay to run a battery right down in voltage to nearly zero, because by about 10.5v the battery is dead flat and will often cop internal damage to the point it can’t be recharged.

This is, of course, a rough guide. A much better and more accurate way to properly measure battery capacity is to fit a proper battery gauge that uses a shunt to measure capacity in and out. These even can give you exact percentage figures about how much power is remaining, but if you work on the voltage method, you’ll have a fairly decent idea.