If you are camping away from mains power then a good battery and charging set-up is essential. Many people simply do nothing more than use the battery provided in their caravan/RV/camper trailer with little understanding of the characteristics of the battery – how much power can it deliver and for how long. A worst case scenario sees a battery becoming fully discharged with a high chance of irreparable damage being done to it. This article will hopefully provide some useful information on batteries, their use and care.
First off, different battery types. There are three main battery types that I will address here, wet cell starter batteries, deep cycle, and a variation on deep cycle that is AGM. It is important to appreciate the differences because they are all made for a specific purpose.
The starter battery is one that we are all familiar with under the bonnet of our vehicle. This type of battery is used to provide very heavy currents to a starter motor for short time periods. Because of this requirement, and thus its construction, it should not be deep cycled as its lifetime will be shortened as the plates will deteriorate rapidly.
A deep cycle battery is one that is NOT designed for short heavy loads but IS designed for the occasional discharge below the 50% threshold (a rule of thumb is that batteries should not be discharged below about 50% of their capacity if you want to get a reasonable life out of them). Deep cycle batteries can be wet cell, but tend to be constructed with the electrolyte more of a gel so that the battery can be “sealed”. Sometimes they are called “maintenance free”, but what this means really is that you CANNOT maintain them because of the sealed nature. In reality, wet cell deep cycle batteries are better in hotter climates because at least you can test the cells and top the electrolyte up with a regular maintenance pattern. Most batteries perform better in colder climates.
AGM (Absorbed Glass Mat) batteries in my opinion are the best choice for camping. Yes they are more expensive, but for the advantages they offer it is worth it. An AGM battery can tolerate the occasional discharge below the 50% level – some people even say down to 20%, but personally I wouldn’t do that. You see batteries LOVE to be charged. They HATE being discharged, and regular excessive discharge is where the damage can be done. AGM batteries tend to charge faster and take more charge, up to close on 100% of charge (did you know that your car alternator is only capable of charging your vehicle battery to around 70-80%?). Because AGM batteries were developed for the military they can take the punishment too. Their sealed nature means that you do not have to vent these batteries to the outside. You can store these batteries inside your car or caravan and even store them on their sides if you have to, and if you leave an AGM battery in storage, unattended for an extended period you can recharge it again without any deterioration or loss of efficiency.
OK, if you are not convinced about the benefits of AGM yet, how about this:
Lifetime of a standard cranking battery is generally up to 4 years
Lifetime of a deep cycle battery is generally up to 6 to 8 years
Lifetime of an AGM battery is up to 10 years
Now of course all this depends on how the battery is used (or abused) and is a general assumed figure if the battery is well cared for. The more you look after your battery the longer the life.
Now on to capacity. The capacity of a battery is usually given in terms of Ampere hours. The best way to explain this is as follows:
You have a 100 Ampere hour battery and you are going to run just one light taking 1 amp from the battery. In the utopian world that light will remain on for 100 hours. However, remember the 50% rule – the battery will best be protected if you run the light for only 50 hours. If you want to calculate the length of stay your battery will reliably sustain you for you need to list all your appliances, their current draw and how long they are used each day. For example if you use two lights drawing 1 amp each for 3 hours per day then your drain is 2×3 = 6 ampere hours.
Then compare your calculations against your battery capacity. As an example, if I work out that all my appliances require 20 ampere hours each day and I have a 120 ampere hour battery then I should be OK for three days. If I have an AGM battery, maybe a little bit longer. Personally I have two 120 ampere hour AGM batteries connected in parallel so I know I have at least 120 ampere hours (the 50% rule), with a bit in reserve. I have tested this on site for three days and used lights, radio, water pump, TV, and experienced no problems at all. I might add here that I also employ a battery voltage monitor to see the state of charge at a glance.
Now how about charging your battery(s). If you have spent good money on quality batteries then please spend a bit more on a quality charger, and the best type is a smart multi-stage charger that will not only charge your battery faster and to a higher charge, but will also ensure a longer battery life with more capacity than if it was charged with one of the constant voltage chargers – you know the type – they sell for around $20.
Where you place your battery(s) depends on their type of course but as I use AGM batteries I have one in the built-in bay in my camper trailer connected in parallel to another that sits in a battery box in the boot of the camper trailer.
If you do use more than one battery, when you connect then together, make sure you use properly sized cable. This is a common mistake made by many people – undersizing the wiring, and then they wonder why their batteries are not delivering. Remember, the smaller gauge the wire, the more voltage loss; and the longer the run, the more voltage loss again. If in doubt, get advice. There is a lot more information on the Internet.
Coming soon – information on Lithium Iron Phosphate batterries for camping.
For more information on dual battery systems (including wiring diagram) for your caravan or trailer see this blog post.
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