Caravan Battery Performance Test

Performance of Different Battery Types

(AGM, Marine, Spiral, Traditional Deep Cycle, Calcium)

After a couple weeks for experimenting with different batteries and test conditions I have decided on the terms of reference for our battery test.

The main thing we are trying to establish is how well certain types of batteries do in real world situations. Our test will involve charge tests with a CTEK 240 volt battery charger which is designed to adapt charging parameters to suit individual battery types.

To perform these tests we will be running the batteries down to 11.5 volts via a 55 watt work light which is rigged up through a Red Arc voltage cut out controller which I have set at 11.5 volts. This basic piece of test equipment will ensure each battery is discharged to the same point which will then allow us to perform fair comparison tests ensuring that each type of battery is compared equally.

Some people may argue that each type of battery has different voltage ranges and that 11.5 volts on one battery may represent a different state of discharge to another type of battery. This is true, however we are conducting real world tests and in the real world if your fridge is designed to cut out at 11.5 volts, then it isn’t going to care what type of battery it is connected to it, the fridge is still going to cut out.

The reason I choose 11.5 volts as our cut out point is that it represents a fair compromise between the ideal voltage you should discharge a battery down to and what people in real use draw their batteries down to. In the ideal world it is generally recommended that you only draw your battery down to 50% charge or around 12.0 to 12.2 volts depending on the type of battery. This generally is never adhered to as many 12 volt compressor type fridges have a battery cut out protection set at 10.5 volts which is well below recommended levels.

Basically the less you draw down a deep cycle battery the more cycles you will get out of it. You really want to prevent deep discharge in your battery usage as this can significantly reduce the life expectancy of your battery. To me 11.5 volts represents a reasonable compromise between the ideal usage of a battery and what is probably going to happen in real use.

Our 240 volt battery charger testing will involve two tests. The first test is to draw the battery down to 11.5 volts and then recharge it with a 25 amp CTEK battery charger for exactly 24 hours. This particular test should give us a good idea of the maximum capacity we can get out of each type of battery and will serve as a benchmark for the other test we will be conducting.

The reason we are leaving the battery charger on for a full 24 hours is that we have found even when the charger indicates the battery is full; how long the charger is left on after this makes a significant difference to final state of charge of the battery. In fact on one test battery we initially left the charger on for around 3 hours after it indicated the battery was fully charged. This resulted in about 25% less available Amp Hours than if we left the charger on for around 18 hours after the battery reached the full charge mark on the charger. To ensure that every battery is given the even conditions to be tested under we have decided that running the battery down to 11.5 volts and then giving it precisely 24 hours on the CTEK charger is the most even way to compare “apples with apples”.

While the 24 hour test should give us a good indication as to the maximum ability of each battery’s potential, people do not always have 24 hours to recharge their batteries. Many people want to be able to quickly recharge their battery by running a generator for a limited amount of time or the batteries are used in dual battery systems where limited charge time is available. This is why we devised the 4 hour test.

In the 4 hour test we will be drawing the batteries down to 11.5 volts and then recharging them with the 25 amp CTEK  battery charger for exactly 4 hours. Once we have done this we then let the batteries sit for 2 hours to dissipate some surface charge and then use our test load (4.6 amps) and data logger to see how many useable Amp Hours have been put into each battery. This should prove to be an interesting test for anyone who uses a generator and battery charger for camping of has a dual battery system.

I must put a disclaimer here that we will not be setting up the battery charger to specifically charge each type of battery. The CTEK charger does automatically sense the type of battery connected to it and charge it accordingly. However, this does not guarantee that the CTEKs charging parameters meet the recommended requirements of each battery manufacturer and we take no responsibility for this. Basically we don’t want to get into complicated solutions, the CTEK has proven itself as one of the best battery chargers on the market and we want to see how each of these batteries perform under general battery charging conditions as many people who are reading this test will already have a battery charger and aren’t going to go out and buy a new one just because some manufacturers require them to! What we want to know is how each type of battery performs on everyday, readily available battery chargers.

The batteries we will be using in our tests represent a fairly broad part of the market. We will be testing a 75Ah Century Deep Cycle battery which has a Calcium composite in the plates; we will also test a full calcium battery which is the M27 Delkor (this is one of the most popular batteries used in dual battery systems). Also in the test is the 75Ah Optima Spiral wound battery (blue top) and the Full River 85Ah Absorbed Glass Mat (AGM) which is also a very popular battery used in dual battery systems. The final battery in the test is the Century Marine Pro 600 which is a dual purpose marine start battery. The reason I have included this battery in the test is the fact that being a start battery it may charge up more easily than a deep cycle battery, and the fact that it has heavier plates than traditional start batteries also means it should do a good job of deep cycling. The AGM and Optima batteries are also capable of being used as start batteries, so it will be interesting to see how they perform in the test. The main concern I have with the batteries in this test is their ability to recharge in dual battery applications, so it will be interesting to see if the batteries capable of starting can charge up better than the traditional deep cycle batteries. It will also be interesting to see if the deep cycle batteries do a much better job of deep cycling than the start/deep cycle batteries.

I picked the batteries in this test because I believe that they represent a good broad section of the market. The problem you come up against in a test like this is trying to compare batteries evenly. Do you compare batteries based on their Amp Hour rating? Their cost? I chose the size as my determining factor. It’s hard to find batteries of different types with the same Amp Hour rating, and then you have to believe the manufacture’s rating, the Marine Pro battery in our test didn’t have an Amp Hour rating. Also batteries with similar ratings can vary significantly in cost and size. In the end I decided to use the physical size of the battery as the determining factor, if it doesn’t fit in the battery tray of my Landcruiser it’s not going in the test.

When you stop and think about it this actually makes sense as in the real world people are interested in fitting the largest auxiliary they can into the limited room they have under the bonnet of their 4WD. My battery tray is about 310mm long so every battery had to fit in, every battery except for the 75Ah Optima that is. The Optima was too long for the tray so I cut a bit out of the end of the tray to allow it to fit. I could have used the next size down Optima, but it was only 55Ah and I really wanted to see how an Optima of similar Amp Hour capacity went against the traditional deep cycle batteries. For those who don’t know the Optima is one of the most expensive batteries on the market at around $450 and has the reputation of being one of the ultimate batteries you can use in a dual battery system, I really wanted to put this to the test so I allowed the Optima in. The thing I want to point out is that the AGM battery even though it had a 85Ah rating (the largest in the test) was also the physically smallest battery in the test.

At the start of the tests I believed quite confidently that the first stage of our test (i.e. recharging the batteries with a 240 volt battery charger for 24 hours) would not show up much difference in the different types of batteries. I believed that the 4 hour test would be the test that sorted out the different types of batteries in real world conditions.

How wrong I was! The individual batteries have been that far apart that I’ve tested and retested to make sure of my results. Another result that I’ve noticed through my continued testing is the significant drop off in the different types of batteries.

When the batteries where new they certainly performed much better than after I put them through repeated charge/discharge cycles. The repeated drawing down of the batteries to 11.5 volts and then recharging them has seen all the batteries drop off from their earlier performances, however some have been affected much more than others!

I have to admit that when I drew the batteries down I tended to leave them lying around discharged to 11.5 volts for a period of 8 to 36 hours before I could recharge them. This is certainly not ideal; however it does replicate real world usage which is the goal of my tests, so I think this observation has been a very worthwhile part of my testing.

All of the different types of batteries where put through these test conditions, so at the end of the battery charger test we can really see which batteries will handle discharging abuse well. This is a very important element for me as my batteries, no matter how hard I try, always seem to sit around discharged for a while.

The perfect example is my 100 Series Landcruiser with my 50 litre National Luna fridge/freezer in the back. I live about 800 metres from work so sometimes I hardly get to take the Cruiser for a long enough drive to get any charge into the auxiliary battery.

The good thing about the National Luna is I can set the battery cut out on the fridge to 9.5V, 10.5V or 11.5V. I really would not like to see any battery go below 11.5 volts especially for an extended period of time, so this is what my fridge is set at. What I want from a battery is to be able to let it sit at 11.5 volts if I cant keep the charge up to it, and then for it to be able to take charge well when it is available.

No battery is going to perform at 100% under these conditions, and if you can avoid them you should! However the real world isn’t perfect and these things do happen, so I want a battery that will cope. Currently I am using a no brand AGM battery that I am considering using for manufacture in a portable power pack sometime in the future. This battery has taken everything I have thrown at it and still performs well, which for me is a vote of confidence in AGM technology.

Another example is our hire fleet of camper trailers. Unfortunately not all hire customers care too much about the condition of the batteries in our camper trailers and there have been occasions where the batteries have been brought back dead flat. Currently our hire campers come supplied with traditional lead acid deep cycle batteries; they have been through the abuse and seem to come back ok when reconditioned on a CTEK battery charger.

Before we changed over to the Cape York camper trailers we where hiring the Kimberley Kampers which came with Gel Cell batteries. These where only good for boat anchors once over discharged, and our bad experiences with them is why you won’t find them in my battery tests. Gels are a great battery if you look after them; however they do not handle abuse well. AGM batteries have similar performance characteristics to Gels however handle abuse much better, and that is why I recommend them to my customers over Gels.

Overall in the battery charger tests I am very happy with the performances of the AGM batteries and marine start batteries. The traditional deep cycle and calcium type batteries really seemed to struggle. Please see the full test results for the different types of batteries here: Battery Test Results