What Size Battery Do You Need For Your Caravan?

Author: Tahlia Maynard   Date Posted:14 December 2016 

Understanding what type of battery your caravan needs is essential before hitting the open road.

Caravanning lifestyles around the world have evolved to incorporate quite a few creature comforts, the kind we typically take for granted at home. Today, it’s pretty common to be exploring the Outback in a caravan containing a TV, refrigerator, air conditioner, water heater and washing machine, to say nothing of sundry lights, gadgets and small appliances. Now, unless you’re absolutely sure that you’ll be parking at sites with access to power, you’ll need to carry batteries along, so you can actually enjoy these creature comforts in your home-on-wheels.

A common question that most people new to the caravanning scene have, revolves around the size or capacity of their new caravan battery. The usual solution to this takes the shape of an online battery size calculator or data sheet with power usage values of most common motorhome appliances. However, before opting for an off-the-shelf solution, it may be a good idea to understand some basics about caravan batteries and how they supply power to your appliances and gadgets.

Car batteries vs. caravan batteries

In theory it is possible to use a typical car battery to power your caravan appliances. However, the way these batteries function requires them to be fully charged at all times, which means you run the risk of getting stranded with a dead battery a few days into your trip. Caravan batteries on the other hand are designed with this exact scenario in mind and follow a use-and-recharge format. There are two types of caravan batteries currently in circulation – absorbed glass mat (AGM) batteries and gel batteries. Of these, AGM batteries are more robust and designed for heavy usage. They are also known as ‘deep cycle’ batteries and have a ‘dry’ design unlike the older wet cell batteries which were susceptible to leakage. Gel batteries are similarly dry and can last even longer than AGM batteries, but they’re very sensitive to voltage fluctuations and therefore need a specially designed charger.

Calculating your caravan’s power usage

A 12V deep cycle AGM battery (by far the most preferred variety of caravan battery) is calibrated in amp-hours (ah). If you see a 100ah rating on a caravan battery, this means that the battery can theoretically provide 1amp current for 100 hours, 5amp for 20 hours and so on. To understand this better a 100ah battery can theoretically power your 10amp hair dryer for 10 hours. You can similarly calculate the duration through which the same battery can power your other appliances. If you don’t know the amp rating of the appliance just divide its wattage by the voltage. A 1.2W light running at 12V will take 0.1amp, and thus run for 1000 hours on your 100ah battery. Your 60W refrigerator will similarly consume 5amp at 12V, but will only be running about 15-20% of the time, which takes its running hour range to 100-133.

However, once we take these considerations to a practical situation, a number of constraints apply, limiting the amount of battery power actually available for use. For starters, the voltage of a caravan battery starts dipping with usage, and the lower the voltage, the less the amperage it can offer. At about 30% charge, an AGM battery is typically unable to power most appliances due to low voltage. Again, all batteries come with a ‘discharge rate’, which for a 100ah battery is usually 20 hours. This means that as long as you’re using less than 5amps of current per hour, your battery should last 20 hours. A heavier usage will take a severe toll on your battery’s performance and capacity, and you would be better off carrying two or more batteries in such a situation.

In summary

The next time you see one of those battery utilisation charts online, focus on how they’re arriving at a usage value instead of just following the usage value itself. Make a list of your major caravan appliances, their wattage or amperage, how much time you’ll need them to run for and how much current would you need to draw at any given point in time. Extend this by the number of days you’ll be camping and you should have a well-informed estimate of the size and number of caravan batteries you’ll need for your next caravanning holiday. If you still have any doubts at all, you can give one of our technical gurus a call on 1800 787 278 and they'd be more than happy to point you in the right direction.