Why LiFePO4 - Are they worth it?
When we reached a stage in our business development where batteries were firmly on the expansion list, we embarked on a journey of what was over 24 months of researching, designing, creating dozens of prototypes, testing, more research, developing new specifications, torture testing here in Oz and reading so much about these things across the industry to work out what customers really wanted, I thought my head would explode. But the more I read and the more testing, charging and analysis and age testing we did, the more I was convinced that LiFePO4 was only option for the future and by far the best option for anyone using their deep cycles batteries daily or on a very regular basis. If you are only a casual user of batteries (ie. once a month for a weekend trip), don’t have any weight issues or simply don’t have the budget for the higher upfront cost, then AGM are still your best option as long as you get the right size. I will use a AllSpark 100ah LiFePO4 and a leading brand 160ah AGM as the examples throughout this article and an average 80ah daily power demand.
Here is why I believe LiFePO4 for “regular daily users” is the way to go. Now there are many people with very strong opinions on this topic, so this is just my opinion based on my research, personal use and testing of both types over many years and in real world scenarios, plus years of customer feedback on using these around the country. This is not a beat up of Lead acid batteries by any means. I use them myself and we sell them too. They definitely have their place for many of users. Both have their pros and cons. We chose to develop LiFePO4 for our AllSpark range rather than AGM for the below reasons.
DEPTH OF DISCHARGE:
Lead Acid (LA) batteries, ie. Flooded, Gel or AGM, Calcium batteries, have a safe Depth of Discharge (DoD) or draw down of 50% to ensure longevity of the battery and avoid premature failure. Why 50%? Well that's the point that the voltage reaches 12v. If you draw below 12V, then the connected loads will draw more amps to compensate for the voltage shortfall, increasing internal temperature and accelerating the rate of discharge. If you were to draw a LA battery down to 20% or lower regularly, you will do significant damage to the cells (through sulfation of the plates or stratification of the electrolyte) and either kill the battery altogether or significantly reduce its life expectancy and its ability to hold much of its original capacity. LiFePO4 batteries can be safely drawn down to 80% DoD or approx 12.5V, without causing damage to the cells and are not affected by sulphation. You should think of this as your baseline and the less you use it, the more cycles you will get. Drawing down to 80% DoD won’t damage the cells or cause premature failure. Think of it as putting km’s on the engine of a car. The more km’s you do the faster it wears out, but at the same time you are also getting more use from it. The other way to look at it is how much use you are getting in terms of total amp hours supplied rather than the number of years or cycles you get. The more ah you use per cycle, the less cycles you get.
WEIGHT AND SPACE:
Using the example of 80ah of battery consumption per day, you will need 160ah of AGM (50% DoD) or 100ah of LiFePO4 (80% DoD) for the same daily consumption of 80 amp hours. An AllSpark 100ah LiFePO4 battery with an exclusive custom designed internal Battery Management System weighs only 10.9kg, versus a leading industry equivalent 160ah AGM at 50.2kg. Whilst this is an excellent AGM battery, it is 5 times the weight and at 200mm longer and 40mm wider, it also takes up almost double the physical volume too. Most Offroad vehicles, whether it’s a 4wd, camper trailer or caravan will all have weight and space constraints and having an option that is half the volume and 1/5 of the weight is a major advantage. Take a sec to think about this same scenario if your daily power consumption was double that (many people do use that much in a day)…the weight requirements would be 20kg vs 100kg
NUMBER OF CYCLES:
Not all batteries are created equal. There are many very good quality options in both chemistry's of battery, but unfortunately there are also some very poor options out there, some still with very high price tags. Our batteries are independently tested by myself 2-3 times per year and a 3rd party audit inspector before they leave the factory to ensure they meet our exacting quality standards and technical specifications and will do what they promise to do. They are also manufactured in a factory that has International Quality Management Standard ISO 9001 certification that is regularly audited for compliance. You can get 3000+ cycles from our LiFePO4 batteries at 80% DoD, 3800 at 50% DoD in excess of 5000+ cycles at 30% DoD. Compare that with an AGM where you will only get around 200-300 cycles (if you don't kill it before hand) at 80% DoD, 400-500 at 50% DoD and around 700-1000 at 30% DoD.
You may have seen prices of some of the popular models of LiFePO4 batteries out there. There are some 12v 100ah batteries priced at over $4000. Yeah, they may have things like Bluetooth cell monitoring and BMS interconnection and a brand name tag, but their design life and cycle expectancy are not that much different to most other quality brands and you are paying for brand name only. At the other end of the scale you will also see some that have a maximum discharge current of only 30-50 amps which is only enough to power a very small inverter (around 500w) and have much lower cycle expectancy. They are cheap and generally made using dozens of low reliability cylindrical cells that once one dies, the rest soon follow due to overcharging to make up for the dead cell.
In the AGM space for a 100ah they range from around $200 up to around $440-$480. 160ah AGM are up around the $550-750 mark and not substantially far off the order of magnitude for changing to LiFePO4. There is a lot of specification variability across the price range, so it pays to do your research first. Look for something that has a C10 rate (10hr rate) in AGM, rather than a C20 rate for the same specified ah capacity. Otherwise its not an apples for apples comparison. LiFePo4 should have a C5 (or 5hr rate). Many cheap batteries have a higher C rate which makes it appear as though it has a higher capacity, but its not really the truth. Some of the cheaper brands even claim higher capacities than they actually really provide. Ask yourself whether you believe it is really possible to fit 120ah into the same physical size case as a good quality 100ah LiFePO4 battery.
Below is a comparison of AllSpark LiFePO4 (4 year full warranty) batteries vs the leading brand of AGM mentioned above (2 year warranty). Both are suitable for deep cycle applications and yes both are also suitable for “under bonnet use” - many LiFePO4 cannot handle under bonnet temps - the 160ah AGM won't fit so it's really only a 100ah AGM that will go into most engine bays and most AGM brands cannot. Most of both types on the market are not suitable for engine bay use, so again, it pays to do your research first. There are many options available, so this is just a comparison of two brands of comparable quality, performance guarantees and warranties. You can see that whilst LiFePO4 is a higher up-front cost vs AGM, if you need it long term and every day, the cost per amp hour and cost per cycle it returns over its life is much lower by as much as 40%. What it does also demonstrate, though, is that it is really important to size it correctly as there is a sweet spot for your specific power usage and getting something too large starts to increase the cost per ah and cycle as you aren’t making good use of the battery (just dead money).
This is where one of the very key benefits of LiFePO4 batteries are totally overlooked by most. Both types when discharged require a “Bulk or Boost” charge where the required charge current is applied until the battery reaches the required voltage. In LiFePO4 the battery will take the recommended charge current (usually 0.2-0.3C) all the way to 100% then stop charging. It will absorb the current at a much faster rate (at around 92-95% efficiency) and get your batteries to full (assuming correctly sized charging systems) very quickly. A LA battery cannot handle full charge current all the way to 100% and it requires many hours of reduced current and constant voltage to achieve 100%. They are also around 70-80% efficient in around cycle charge acceptance needing more power to recharge the same amp hours each day.
What does this mean? If you were to have 400w of solar, for example, putting out an average of about 20 amps per hour it would take approx. 4 hours in the morning to return your LiFePO4 to 100%, then go into monitoring or maintenance mode. There is a technical argument about the best no load (float) charge levels for LiFePO4, but that is a whole other article and will bore most people to tears. Drop me a line if you want to learn more. Using the same solar output, the AGM will complete the bulk charging stage in a similar time frame to around 80-85%, but the absorption stage where current to is reduced to much lower amperage, with voltage kept stable, can take another 4-6 hrs to get your batteries all the way to 100%. This equates to poor utilisation and efficiency of solar and the need for more solar watts compared to LiFePO4. You still need the 400w size (in this example) to provide the bulk charge in the morning so that you have the rest of the sunlight hours to complete the charging process. With LiFePO4 it will take whatever current you give it (within the design parameters) until it’s almost full then tapers off (tail or termination current) to 100%. As it achieves 100% in a much shorter time frame with less overall energy, you can therefore reduce your solar requirements compared with that required for AGM.
If you are using your batteries every day, or regularly camping off-grid for long periods of time, then LiFePO4 is by far the most cost effective, long term option. If you only use it once a month, stick with LA unless you have a weight or space issue. Yes, they are more up front, but less per ah and per cycle over the long term. You will also need less solar watts as it charges at a faster rate, takes up less space and also results in less weight in your vehicle with LiFePO4. It gives you more usable ah in the same size battery or allows you to have much less ah capacity overall.
This can be a very complex topic and I have tried to summarise the key points about the benefits of Lithium Iron Phosphate batteries in a simple format. I hope it helps those of you just getting started with your own research or just can’t quite get your head around it all and need a helping hand. If you have any questions, please feel free to post them up. As always, I welcome feedback. If you have something to add, or you think something needs correcting, please let me know. I am not the world’s most experienced expert on LiFePO4 batteries but have done more than enough research and testing over many years to make my head explode. However with thousands of AllSpark batteries around country, we do like to think we know what does and does not work if pretty much all scenarios.
There is a lot more technical information on this, but this is the basic version.
Hope this helps. Shout out if you have any questions.
Catch ya Offroad