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Lithium vs AGM Batteries for Deep Cycle Use

Deep Cycle Lithium Iron Phosphate (LiFePO4/LFP) Batteries: Everything You Need to Know

If you're looking for a battery that can provide long-term power, you should consider deep cycle Lithium Iron Phosphate (LFP) batteries. Unlike other batteries, lithium (LFP) batteries are designed to be discharged and then recharged multiple times and they can also provide a steady supply of power for an extended period before the voltage drops away effectively, allowing you to use up to 85% of the battery’s rated capacity.

This makes them perfect for caravanning, motorhoming, camping, boating, electric vehicles, and appliances. In this article, we will also discuss lithium vs AGM batteries and everything else you need to know when you're choosing batteries.

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What Is an Absorbed Glass Mat (AGM) Battery?

Absorbed Glass Mat (AGM) batteries are made up of plates and separators that are soaked in sulfuric acid that is absorbed in the fiber glass mat separator. This creates a spill-proof battery that can be mounted in virtually any position.

There are two versions of AGM batteries – Standby power for float charging applications such as UPS and then there are deep cycle batteries designed for regular deep discharges and can be recharged and discharged multiple times. They are a popular choice for solar applications, as well as campervans, boats, and electric vehicles.

Deep cycle batteries are different from standard car starter batteries because they can supply power steadily over time. If you think about a standard car starter battery, you only need to use it for a couple of seconds as it provides a burst of power to the vehicle. The battery is then recharged slowly as the car runs. However, AGM batteries will continue to supply power for up to several hours before you need to recharge them.

What Is a Lithium (LFP) Battery and How Does it Work?

There are commonly 2 forms of lithium (LFP) batteries so to eliminate confusion, here is a brief description of them.

  • Lithium Ion: These batteries contain two combined chemistries for the cathode of either lithium cobalt or lithium manganese, and both commonly use a graphite anode. These combined chemistries present the advantage of higher available instant energy but are stressed heavily with heat, making them more volatile. However, when used in the correct application and with the right controls (i.e. charging source and surrounding heat), they can be safe and provide the right balanced energy for power hungry appliances including where small cells are required. Typical voltages are in 3.6V cells or series up from there.
  • Lithium Iron Phosphate (LiFePO4/LFP): These batteries have a cathode mode of iron phosphate and a graphite anode. They’re designed with a balance of consistent energy delivered over time (i.e. deep cycle applications running loads such as 12V fridges, lighting, inverters and electric outboards over a 12 to 24 hour period). They’re safer to operate in temperatures up to 60° but deliver more energy and recover better when in the 15-30° temperature range. This chemistry is more sought after by customers as an alternative to AGM batteries in lightweight quick recovery applications such as caravans, motorhomes, 4WD (not engine bay) and boots.

It is important to note that both Lithium Ion and Lithium Ion Phosphate (LiFePO4/LFP) batteries require a Battery Management System (BMS) built into them when they are manufactured in a capacity greater than 3.6V for several reasons.

What Is a Battery Management System (BMS) and Why Is it Needed?

The Battery Management System (BMS) performs the function of allowing and controlling the flow of discharge and charge currents as well as managing intercell balancing of the internal cells linked in series and parallel. This is vital to obtain maximum capacity and service life.

It also serves to protect over-discharge by cutting supply internally if the discharge current exceeds the rated capacity of the BMS (i.e. 100A BMS and inverter size of 2000W of 12V is used of that capacity = 166.66 amps which is too much, so to ensure internal cabling and BMS is not stressed to the point of a safety issue, the BMS will cut power supply from the internal cells).

This is the same action for over-discharging overall where for example, the voltage of the 12V battery bank is taken down past 10.5V.

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Differences Between Lithium (LFP) and AGM Batteries

Lithium (LFP) and AGM deep cycle batteries are both cyclic batteries, but there are some key differences between them.

The first difference you'll probably notice is cost. Lithium (LFP) batteries are more expensive than AGM batteries. However, they also have a longer lifespan and can provide more power in a smaller and lighter package.

AGM batteries are typically better at handling large current loads than lithium (LFP) batteries. So if you're using your battery for applications such as starting a boat engine, then an AGM battery is probably the best option.

Lithium (LFP) batteries are better at providing long-term power than AGM batteries. This makes them a popular choice for appliances, electric vehicles, and other applications where a steady power supply is needed.

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Advantages of Using a Deep Cycle Lithium (LFP) Battery

There are several advantages to using a deep cycle lithium (LFP) battery. Some of the most notable benefits include:

  • Long Lifespan: Lithium (LFP) batteries have a much longer lifespan than other batteries. This makes them an excellent choice for applications where durability is important.
  • High Energy Density: Lithium (LFP) batteries have a higher energy density than other types of batteries. This means that they can store more energy than other batteries, making them perfect for use in applications where long-term power is needed.
  • Low Self-Discharge: Lithium (LFP) batteries have a low self-discharge rate. This means that they can be stored for long periods without harming the cells.
  • Lightweight and Small: Lithium (LFP) batteries are lightweight compared to AGM batteries, as they don't contain heavy lead acid. This makes them easy to transport and install.

Disadvantages of Using a Lithium (LFP) Battery

While lithium (LFP) batteries have many advantages, they also have a few disadvantages. Some of the most notable disadvantages include:

  • High Cost: Deep cycle lithium (LFP) batteries are more expensive than other types of batteries. This can be a significant drawback for applications where cost is a factor.
  • Limited Power Output: Lithium (LFP) batteries have a lower power output due to their BMS than other batteries. This can be a problem for applications where high power is needed (i.e. larger inverters and cranking applications).
  • Temperature Sensitive: Lithium (LFP) batteries are sensitive to high temperatures. This means that they must be stored and used correctly, otherwise they may not work well, or the expected life/capacity is shortened.
  • Quality: Not all manufacturers use quality cells, quality BMS or put a sufficient heat sink/cable size in place leading to premature failure and possible catastrophic failure. You can’t look inside the battery to see if this is the case.

How to Choose the Right Battery for Your Needs

When it comes to choosing a battery, there are a few things you should consider. Some of the most important factors include:

  • Application: The first thing to consider is what type of application you will use the battery in. This will help you determine the correct type of battery for your needs. For example, lithium (LFP) batteries are typically best for appliances, electric vehicles, and other applications where a steady supply of power is required. In contrast, AGM batteries may be better for applications such as starting a boat engine.
  • Power Requirements: The next thing you should consider is how much power the battery will need to provide. This will help you determine the right capacity and type of battery. You also need to consider whether there’s a need for 1 to 2 days extra storage of power as AGM’s are commonly cycled to a maximum of 50% depth of discharge (DOD).
  • Temperature: The temperature of the environment where the battery will be used is also essential to factor in. Deep cycle lithium (LFP) batteries work best in a moderate climate. However, if you live in an area with extreme temperatures, you may need to choose a different type of battery.
  • Lifespan: The final thing to consider is how long the battery will need to last in the proposed application. This will help you choose a battery with the most suitable lifespan.
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Final Thoughts on Lithium (LFP) Batteries

Lithium (LFP) batteries are an excellent choice for applications where reliability and durability are important. They have several advantages over other types of batteries, including low maintenance, long lifespan and power output, and light weight.

However, lithium (LFP) batteries aren't always the best choice. They can be expensive and have a limited power output (due to BMS restrictions). They also require a moderate climate to work correctly, don't work well at very low or very high temperatures and not all lithium (LFP) batteries are made equally which leads into the warning that we often see through life.

You Get What You Pay For

So, buyer be aware, do your research.

If you're not sure what type of battery you should buy or have any more questions about batteries, feel free to contact our knowledgeable staff at A1 Batterypro. We'll be happy to give you further advice on choosing the right battery for your needs.