Previously, I did a very unscientific test using a 100ah deep cycle AGM battery and my 78L ARB fridge. Since then, I have been contacted by a representative of Ark and given some great information on what you might need to know about your ARB Fridge and battery life.

Do you own an ARB Fridge? Or any car fridge for that matter… Did you know that you probably shouldn’t run it from your car’s battery for too long? Draining your cranking battery will severely limit its life span. In this article, I’ll lay out the information that was given to me by Ark. Hopefully, it makes sense!

How is battery capacity measured?

Basically, battery storage capacity is measured in Amp hours (Ah). So if you have 2 x 12V batteries, a 100Ah battery and a 50Ah battery, the 100Ah battery will deliver 12V of power for longer (can you guess how long?). Which means you can power your car fridge for longer between charges.

An amp hour (Ah) rating is just what it sounds like – the number of hours a battery can provide 1 amp of current at 12 volts before the battery is completely dead. NOTE! This metric is not completely accurate! But it does provide a good way of comparing one battery to another. So now we have some kind of understanding of Amp hours, right?

A crucial element to understand when it comes to batteries is the difference between deep cycle batteries and cranking/starter batteries. Your cranking battery is the one that was delivered under the bonnet of your car when you purchased it from the dealer. Its purpose in life is to deliver a huge amount of power for a very short time. Once your engine is running, it maintains that full charge. Whereas a deep cycle battery is designed to deliver low amounts of power continuously for a longer period. So comparing a 100Ah deep cycle battery and a 35Ah starting battery doesn’t make any sense. They’re two different batteries designed to do different things.

Deep-Cycle vs Starter Batteries and Your Car Fridge

Pretty much all cars have a “starter” or “cranking” battery. This is the one that delivers the power to turn your engine over until it fires up. On those cold mornings when your engine won’t start and you hear that “RehRehRehRehReh” while you sit there saying “C’mon! C’mon! C’mon! Start damn-it”. That’s all on battery power. Do it too long and pretty quickly your cranking battery runs out. Starting your car requires a burst of 100 to 200 amps. And 300 amps isn’t unheard of. Your cranking battery is designed to deliver it for a short period of time.

Which is why running your car fridge off your cranking battery isn’t the best idea. The same applies for anything that you use for a long time while your car isn’t running (camp lights for example). If you over-discharge your cranking battery more than a few time then it rapidly stops being able to hold a charge at all. Cranking batteries can’t be discharged more than about 25% before their lifespan is depleted.

Your typical deep cycle battery, however, is designed to store energy and deliver it at lower amperages for longer periods of time. Most can be discharged to 50% of their capacity before their life is compromised. And some of the best ADM or Lead Acid batteries can be run down to 75% of their maximum charge without damage. So these are the guys you want to be using to power your car fridges, camp lights etc. You might think of deep cycle batteries as marathon runners, and cranking batteries as sprinters.

How To Power Your ARB Fridge Freezer Without Killing Your Vehicle Battery

Well… Really… the simplest answer to this question is… Use a separate battery to power your fridge. Your starter battery may well be able to manage the load over the short term, you will eventually ruin it. This is not only expensive but if you’re in the middle of the bush and can’t start your car it can be inconvenient at best and life-threatening at worst.

The best solution is to get a deep cycle battery, drop it into a good quality battery box (like one of the ArkPack ones) and power your fridge from that. The table below gives you an indication on how long you might be able to run it for without recharging.

NOTE: These are theoretical maximums. Lots of factors will affect these times. For example, these times assume you discharge the deep-cycle battery 70% (30% of total charge remaining), and they assume that your battery has 100% of its’ listed capacity. I’d suggest taking a few hours off each estimate just to cover yourself. I don’t want you’re cursing my name when your beer goes warm! That’s way too much responsibility for even my humungous, muscular, Adonis-like shoulders.

Where to put your Deep Cycle battery

There are a number of options here. Many people install a second battery under their bonnet right next to the main cranking battery. That’s fine if you have space up there. I found a place behind the trim in my boot to put mine, but for a while I had it in a battery box so that I could remove it if I wanted to.

The battery box I used was a dumb box. It basically held my battery and told me how much charge was remaining. But the ArkPak battery box is a much smarter unit. It includes a top-notch battery charger/conditioner to keep your battery in good shape. It also includes the relevant cable work so that you can mount your ArkPak in your vehicle just as you would a dual battery. And it also includes an inverter that converts your 12v into 250v.

That’s handy if you need to power things like laptops etc. In addition to this, the built-in, easy to read, digital meter lets you know when your battey is ready to be charged up again and an audible alarm warns you as your charge drops away. Given that a good quality AGM battery is expensive, why wouldn’t you want to get the most life out of it? Makes sense to me!

As you might expect from a quality batter box, it does more than just run your ARB car fridge. You’ll also find that 240v socket for powering the laptop, coffee machine, or foot spa. You’ve also got a number of 12v power sockets and also a built-in USB port for charging your mobile devices. Now that’s a handy idea!

So I hope this article helps you out with working out not only what kind of battery you need to run your fridge, but also how to actually take your battery with you!