In this day and age, people want all the luxuries of their own home to be available and ready to use when they are away camping. So for appliances like fridges, microwaves, TV’s and other household gear, we obviously need something to power them. This power most commonly comes in the form of a 12V battery, whether it be an AGM, Calcium or Gel etc. these batteries are easy to get your hands on and are readily available at most battery stores, but what size battery or battery bank do you need for your specific needs?
To help you figure this out, we have created a list of FAQ’s or frequently asked questions to help answer some of the queries that you may or may not have.
1. What size battery do I need?
This question is probably the most frequent question we are asked and its very simple once you can wrap your head around it. To work out what size battery you need you first need ask yourself a few questions, “How long will I be going away for at any one time?”, and “What will be my power draw over the course of 1 day?”.
If you're a weekend camper, having a massive battery or battery bank is not quite as critical as someone who will be doing a lap of the country. So for most weekenders a 120AH battery is more than enough to power your fridge and LED lights for a night or two.
For more serious campers it becomes a lot more critical to make sure that you have enough battery storage so you are not left stranded in the middle of nowhere with no power to run your appliances. This is where you will need to know your maximum power draw over the course of 1 day. Once you know how much power you will be using you can then work out the size of the battery bank you will need.
To work this out, simply gather all your appliances together and find the Current or Amperage draw. Most appliances have this in their specifications or on a sticker on the back of the item.
Then work out how long you normally use the items for and multiply this draw by that many hours.
Finally, use some simple addition to add them up!
12V Fridge- 2 Amps per hour over 24 hours of use =48 Amps (round up for safety) = 50 Amps
12V LED Lights- 1-2 Amps over 5 hours of use = 5-10 Amps
12V Water Pump- 5-10 Amps over an hour of use = 5-10 Amps
12V TV- 5 Amps over 3 hours of use = 15 Amps
Overall usage for 24hrs- 75-80 Amps
Suggested size of battery bank- 240-320AH
Your battery bank should be at least 3-4 times your daily usage to ensure you aren’t draining your batteries too low. This also allows for a few days of bad weather if you are charging with solar. Now of course everyone has different appliances in their systems and these calculations will have to be customized to workout what your personal system requires.
2. How long will this battery run my appliances for?
This question has a lot of similarities to the previous, and has many of the same principles. There is loads of false advice wherever you go and a common misconception is that because you have a 100AH battery, you will be able to run a 1amp LED strip for 100 hours. This is certainly not the case with most battery types and especially AGM’s.
To get the longest life out of your battery you must drain it as little as possible each time you use it. This is why we suggest to not drain your battery below 50% over the course of its lifetime if possible.
So this means that if you have a 120AH battery, and your overall usage for 1 day is 60AH. You can run your appliances for 1 full day before you must start to recharge or you risk damaging your battery life.
3. What size battery charger do I need for this battery?
The general rule of thumb for battery charger size is 10-20% of the battery amp hours.
So if you have a 120AH battery, a 12-24 Amp charger is the ideal size to keep the battery healthy.
Now, most battery chargers are ‘smart’ battery chargers and are designed to keep your batteries as fully charged as possible without overcharging them. In saying that, having a 40amp battery charger topping up a 100AH battery will do damage to the battery and is not recommended at all.
Therefore, we recommend to size your battery charger around 10-20% of the overall amp hours of your battery or battery bank.
For older vehicles, you can use your own cars alternator to charge your auxiliary battery via a VSR (Voltage Sensitive Relay). This is the most basic way of charging a car battery with a running car. Unfortunately, these units became much less effective on newer cars as in 2007 most vehicles started to have 'Smart' alternators.
For newer vehicles we recommend a DC-DC battery charger which is the next step up from a VSR. These are designed to keep your batteries as fully charged as possible whilst monitoring charging levels to prevent overcharging. They do this by smoothing the variable output from a smart alternator and transforming it into an exact charge profile to match what the battery requires.At the same time, they’ll also operate as a voltage sensitive switch and MPPT solar charge controller. Hence why they are considered so powerful and handy.
Additionally, you could use a solar panel to top up your battery charge. However, you are not supposed to connect a solar panel to any battery without a solar regulator. Failure to do so will provoke irreparable damage to your battery.
4. Can I crank off this battery?
At Australian Direct we specialise in 12V AGM Deep Cycle batteries and have done so for years now. AGM batteries are the industry standard for caravanning and camping and are perfect for running appliances that would usually only be usable in the comfort of your own home. So we know that they are excellent at running appliances, but a common question we get is ‘Can I crank off this battery’? Short answer is NO.
AGM batteries are not made to be used as cranking batteries or have a high draw taken from them over a short period of time. Infact if used for this purpose it will indefinitely damage the battery and most likely kill it. If you need to crank off an AGM battery in an emergency then so be it, but they aer not designed for consistent cranking use.
5. Can I lay these batteries on their side?
Conventional "wet" style batteries should never be mounted in any orientation other than upright since there is liquid electrolyte inside that could escape the battery.
Maintenance-free, absorbed glass mat (AGM) style batteries offer more flexibility regarding mounting angles because the electrolyte is absorbed, not flowing freely. This means you can mount these batteries on their sides or end on end, without affecting the performance and life expectancy of the battery.
This comes in very handy for customers who wish to place batteries under their car seats or lay them down in a tricky position under their tray.
6. Can I link a new battery into my existing battery system?
This question is hard to answer as there is no simple yes or no answer. The outcome is determined by the owner of the batteries, and how they have treated them. This needs to be a completely honest consideration.
Batteries weaken over time and slowly lose the ability to hold as much charge as what they were originally capable of at the start of their life.
For example- A 120AH battery after 2 years of being drained to 50% each use, might now only be a 80AH battery.
So what would happen if I linked my new 120AH battery with this older 120AH (80AH) battery?
Well, when you link 2 batteries together they will want to share each others power and equalise. The older battery drawing on the newer battery means it cannot stay charged as it would like to and over time will effectively be an 80AH battery. This is not ideal by any means and in the long run it can damage your new battery due to not receiving a full charge. This is why we recommend not connecting batteries together that have more than 6 months age difference.
So obviously if you haven’t used your battery much in the last 6 months and you have looked after it, there would be no issue adding another battery to your bank as long as it’s in good condition. However, if you have given your battery a good workout then it’s best that you don’t add another battery after the 6 months.
Other than this, some more crucial things to check is that both batteries are the same AMP HOURS, same chemistry (AGM, Calcium, Lead Acid etc), and if possible the same brand.
7. Can I Mount AGM Batteries Under the Bonnet?
It is a common misconception that AGM batteries can be mounted under the bonnet and used as secondary batteries. This is not the case as AGMs are completely sealed, maintenance free units and cannot handle high temperatures.
AGM batteries can tolerate up to 60 degrees. However, these higher temperatures degrade the battery shortening the service life.
Many modern vehicles are equipped with a Turbo, this means engine bay ambient temperatures easily exceed the 60 degrees damaging the battery. Therefore it is recommended to relocate the battery to the cabin, canopy or tub/tray of the vehicle.