If you own an ARB fridge freezer, or you're thinking about buying one, you might be wondering how long you can plug the fridge/freezer into your vehicle without risking a dead battery. We can help you figure that out, as well as give you some background info that will help you with other questions you have about powering electrical devices off your vehicle's battery.
First, Here's How Battery Capacity Is Measured
If you want to know how much energy a typical 12V lead-acid vehicle battery can store, you want to learn the battery's amp hour (Ah) rating. More amp hours means more total storage capacity, or more time you can plug in your ARB fridge without a problem.
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. While this rating isn't 100% accurate (you can't completely drain a lead acid battery, at least not without ruining it), it's a good metric for comparing one battery to another.
However, it's crucial to understand the difference between deep cycle batteries and starter batteries (aka cranking batteries) whenever you're evaluating a battery's Ah rating. Deep cycle batteries are designed to provide low amounts of power continuously, but starter batteries are only designed to provide a lot of power for a very short time. Comparing a 100Ah deep-cycle battery to a 35Ah starter battery, for example, is silly. They're two different batteries designed for different jobs.
Deep-Cycle vs Starter Batteries and Your ARB Fridge
Almost all vehicles have a "starter" or "cranking" battery as standard equipment. This is because your vehicle's starter requires considerable power (100-200 amps of current draw is normal during start-up, 300+ isn't unheard of), and a battery that's designed exclusively for this purpose is both efficient and affordable (generally speaking, starter batteries are less costly than deep-cycle batteries). Starter batteries are by far the most common battery type, and what most vehicle owners are familiar with.
However, starter batteries aren't the best choice for running your 12V fridge/freezer. This is because over-discharging a starter battery is a great way to kill it. As most of us know, you can only drain a starter battery a couple of times before it stops holding a charge. Generally speaking, starter batteries can't be discharged more than 25% before their lifespan is compromised.
Deep-cycle batteries, on the other hand, are designed for energy storage. They can be discharged up to 50% without any loss, and some of the best deep-cycle AGM or gel lead-acid batteries can be discharged 75% without any loss of battery life. Because deep-cycle batteries are ideal for storing energy, they're used in all sorts of storage applications, from RV battery banks to marine trolling motors to solar energy storage systems.
To use an analogy, deep cycle batteries are marathon runners, while starter batteries are sprinters. You want a deep cycle battery for your ARB fridge/freezer.
How To Power Your ARB Fridge Freezer Without Killing Your Vehicle Battery
If you want to know how to power your ARB fridge freezer without killing your starter battery, the answer is to use a separate battery to power your fridge. While your starter battery might be able to handle the load over the short term, you risk ruining the battery if you leave your fridge plugged in too long. This is especially true if you're using a small starter battery and/or if the battery you have in your vehicle is more than a few months old.
As far as setting up a second battery just for your fridge, you can buy a quality deep-cycle battery. Then, drop it in a good quality battery box (like this one), and then use the following data table to help you figure out how long you can run your fridge before it's time to recharge the battery in your battery box.
|ARB Fridge/Freezer Size
|Current Draw (Amps/Hour)
|60ah Deep-Cycle Battery
|80ah Deep-Cycle Battery
|100ah Deep-Cycle Battery
|37 Quart/35 Liter
|50 Quart/47 Liter
|63 Quart/60 Liter
|82 Quart/78 Liter
NOTE: 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. Therefore, you should view these times as theoretical maximums and discount them a few hours to make sure you don't ruin your battery by over-discharging it.
Why Pairing An ArkPak With Your ARB Fridge/Freezer Is A Good Idea
While you can use a battery box along with a deep cycle battery to run your ARB fridge/freezer, it's not an ideal solution. This is because battery boxes are often "dumb" - they don't have any circuitry to monitor your battery's capacity to make sure you don't over-discharge it, nor do they have any sort of conditioning circuitry to maximize battery life. Our battery box has a conditioner, but it doesn't have a readout to indicate how much longer you can run your fridge without risking your battery.
The ArkPak is a "smart" battery box, as it includes a sophisticated battery charger/conditioner, circuitry that allows you to mount your ArkPak in your vehicle just as you would a dual battery, and an inverter that's handy if you need to power more than just your ARB fridge. Most importantly, the ArkPak has an easy to read digital meter that tells you when it's time to recharge, and an audible alarm that warns you as your battery charge level drops. This prevents you from over-discharging.
Considering how much a quality AGM or gel deep cycle battery costs (especially one with 100ah of capacity), you can't afford to ruin it by over-discharging it. An advanced battery box like the ArkPak is a smart investment.
Finally, the ArkPak can do more than just run your ARB fridge. It can also provide power to your personal electronics thru the built-in USB port, can power appliances that run on 110V AC power (like LCD TVs, laptops, and other low wattage items), and it has multiple 12VDC cigarette lighter plug-ins for 12V appliances (like camping coffee makers, air mattress inflators, etc). The ArkPak is popular with campers, boaters, tailgaters, people who need power in remote cabins, etc. It's a handy tool, so be sure to check it out.