Comparing LiFePO4 batteries to the traditional lead-acid type batteries

 

Better battery performance?

Here at Solar Technology International, we want you to get the most from the leisure batteries that store the energy generated by your solar panels, so we recommend the Lifos Go range of advanced lithium batteries. In this article, our technical team compares the properties and performance of traditional lead-acid batteries with lithium iron phosphate (LiFePO4) batteries.

Here's a brief summary of our conclusions. Read on for all the detail.

Which battery do I need?

There are a lot of different choices when it comes to choosing the correct leisure battery. Even after you have decided on which of the battery types to go for, there are multiple choices withithat category that will affect the quality of your experience. Some batteries can do a high number of charge cycles but not at a high depth of discharge, whilst some will offer a low self-discharge rate but at a higher cost.

So, how do you decide which is the right battery for you? Well, we hope by explaining some of the terminology used when talking about batteries, you will have a better understanding of which features will matter most to you and therefore which battery type would best suit your needs.
Let’s dig in ……

 

What is the usable power?

The Depth of Discharge (DoD) determines how far the battery can be discharged before needing to be recharged, and therefore how much power you can get from the battery. This is effectively the usable power of the battery for your leisure needs.

The Depth of Discharge metric that is still used today is based upon a 50% DoD because most lead acid batteries can only be 50% discharged. To keep a level playing field for comparing all batteries, the 50% DoD standard is the one that is generically referred to, even though many modern batteries can exceed this.

What is a battery cycle?

The metric used to compare all batteries is a battery cycle. A full battery cycle is traditionally seen as a 100% charged battery being discharged down to 50% and then charged back up to 100% again. How many times you can charge/discharge your battery, determines the cyclic lifespan of the battery, and ultimately when it will need to be replaced.

What is a cyclic lifespan?

This is the number of charge/discharge cycles a battery can make before its capacity drops below 50% of its rated maximum capacity. As an example, let’s consider a 100Ah battery with a cyclic lifespan of 500 cycles. After 4 years of use it has completed those 500 charge/discharge cycles, so it now only has a maximum capacity of around 50Ah. Consequently, you would find that it wouldn’t last very long, compared to when it was new.

The overall capacity of a battery is affected by its age, how rapidly it has been charged/discharged, and how many charging cycles it has been through. The older the battery, the more heavily the battery has been used and the more often it has been used, which will all determine how much cyclic lifespan is left.

Eventually, the battery wears out over time when it is no longer capable of storing the amount of power it did when it was new. This is a chemical limitation and affects ALL batteries, no matter their composition.

Using this 50% metric, a LiFePO4 battery could deliver over 5,000 cycles in the battery’s lifetime, which is substantially longer than the lead acid types. Additionally, LiFePO4 batteries can deliver a 90% discharge capacity, meaning a 100% charged battery is discharged down to 10% and then charged back up to 100% again. Lead-acid type batteries simply cannot deliver this level of performance, so if you want lots of power lithium is the way to go.

Ultimately, this means that LiFePO4 batteries have a lifespan of almost twice as long as the lead acid types at the higher 90% discharge rate, or almost ten times longer at the 50% rate.

Is there a difference between a standard leisure battery and a deep-cyclic leisure battery?

In a word, yes, but depending on your device usage it will determine if a deep cyclic battery is the right one for you. Traditional sealed lead acid types are fine if you only need light use of your stored leisure power, e.g. less than 20% between charges. This type of battery may also be best for you if you normally use electric hook-ups when staying overnight.

If you intend to use 20-50% of your battery power between charges or want to avoid the use of hook-up power as much as possible, then a deep-cyclic leisure battery is the way to go. As lithium batteries have a deeper cyclic lifespan than lead acid batteries, then for longer periods of being “off-grid” these are the best batteries for this use case.

What is the C-rating?

The C-rating is how fast you can draw current from the battery and how fast you can charge it. As an example, a 100Ah sealed lead-acid battery may allow you to draw 10 Amps for 5 hours until it reaches its DoD limit (10A x 5h x 50% DoD = 50Ah).

The rate at which you can discharge a battery is not always the same as the rate at which you can charge it, and whilst each manufacturer has their specific guidelines, a generic rule of thumb for lead acid batteries would be 10-20% of the battery rating (10-20A for a 100Ah battery)

Lithium batteries have a much greater capacity for using the available power within them, which is managed by a battery management system (BMS) that is built into the battery, so their C-rating tends to be higher. As an example, the Lifos 105Ah battery can be charged/discharged at a rate of 30-50A without affecting the battery's performance or lifespan.

Which battery is better value for money?

Initially, the sealed lead-acid battery is by far the cheapest battery to buy outright, then the AGM, then the gel, and at the top end of the scale, the LiFePO4 battery has the highest initial purchase price.

However, when you compare the cyclic lifespan and depth of discharge to the cost of the battery, you may find that you would need 2 lead acid batteries to give you the same amount of usable power as a lithium battery and you would have to replace them 3 or more times in the same 10 years you had a lithium battery installed. This is a 6:1 replacement rate for lead-acid batteries compared to lithium for the same power availability, over the same time.

Payload/weight

Additionally, there is a weight saving to consider here and the knock-on effects of that too. If you have 2 lead acid batteries in your motorhome to give you the same capacity as a single lithium battery, that could easily mean carrying over 52kg in leisure batteries. That would amount to around 40kg more than the equivalent power and weight from a single lithium battery. If you removed 40kg of weight from your motorhome to keep under that all-important 3.5-tonne limit (standard car license), you have just reduced the weight of the vehicle by over 1%. Think about how much would you save in fuel costs in those same 10 years as well!

 

Maintenance

Unless you have the older-style flooded lead-acid cells, then most batteries these days are “maintenance-free” whilst in use, as they are experiencing a level of charge/discharge each day. The same is not true when batteries are left in storage, so it is important to follow the manufacturer’s guidelines about how often to check the battery and when it should be charged.

As with all chemical batteries, if they are stored for extended periods and not looked after correctly, there is the potential for permanent damage to be caused to the battery. This may render the battery useless and void your warranty, so it is important to check on the battery if it is not in use / in storage.

As an example for the Lifos 105Ah battery, it is recommended to turn the battery off using the inbuilt switch when it is not in use, and then check/recharge it every 3 months when kept in storage.

Additional features

One feature that lithium batteries with a battery management system (BMS) have, is the ability to communicate what the battery state is over Bluetooth to an app you can install on a mobile device. This feature makes it simple to check voltage, current, the state of charge (SoC) of the battery and whether it is being charged/discharged, without the need to get into the battery compartment with a multimeter and take readings by hand.

An app is a great tool to have, and it does make checking up on the battery simple but having access to a multimeter for fault-finding across the vehicle is always a good idea.

In conclusion

Whilst it is undeniable that the lithium battery does cost more upfront, ultimately, if you can afford the initial outlay of a LiFePO4 battery, it is 2-3x lighter so it’s easier to handle, less hassle as you don’t have to change it as often, you don’t need access to it to check on its performance as it has a BMS with Bluetooth, it is genuinely cheaper to run as its cost per charge cycle over its 10+ year lifetime is substantially cheaper than its lead-acid competitors, and it saves money on your fuel costs!

We hope this article has been helpful, and if you want to look at our range of LiFePO4 batteries, you can do so by following this link - https://www.solartechnology.co.uk/category/lifos/1/

If you need any further information, or would like to discuss your specific needs in detail, please contact our Technical Team by emailing support@solartechnology.co.uk