LiFePO4 Battery Cycle Life & Durability

Cycle life is the best way to evaluate how long your battery will last. In fact, cycle life provides a more realistic view of the lifespan than the estimated number of years.

LiFePO4 batteries are the best that lithium batteries have to offer right now. People new to this technology often question, ‘what is the cycle life of LiFePO4 batteries’. This value is not the same for all lithium-ion batteries.

This article will talk about the cycle life of LiFePO4 batteries. It will also tell the various parameters that affect the cycle life.

What is LiFePO4 Battery?

The LiFePO4 battery is an evolved form of a conventional lithium battery. It has Lithium Iron Phosphate (LiFePO4) as the cathode material. The anode is made of graphite. These batteries have overtaken the market of rechargeable batteries. They last ten times longer than any lead acid battery. Their performance characteristics are even better than conventional lithium batteries made of other materials.

What is the Cycle Life of a LiFePO4 Battery?

Good quality LiFePO4 batteries can easily last for over 5000 cycles. This value is calculated at 80% Depth of Discharge. ‘Good quality’ is the main keyword here, as the cycle life can vary significantly between manufacturers. Eco Tree Lithium batteries come with a 6-year warranty, last for a minimum of 4500 cycles, and remain in optimal health. At the same time, local LiFePO4 batteries can show end-of-life signs after just 2500 cycles.

The cycle life that the manufacturer provides with the battery is just an approximate indication. The actual cycle life can vary significantly based on many factors. These factors will be discussed in the later sections.

How Long is 1 Battery Cycle?

One battery cycle is the time taken to reach from charged to discharged state. A battery cycle can be as long as 1 hour for one battery. For another, a battery cycle can be 10 hours.

Understanding the ‘discharged state’ is another important aspect here. The discharged state does not mean that the battery will reach 0% charge. The discharge state is where the battery shouldn’t be used further as it will degrade the health. This is defined by the battery’s Depth of Discharge (DoD).

If a battery has a Depth of Discharge of 80%, it will be discharged at a charge level of 20%. After this value, it requires charging again.

How Many Cycles Do LiFePO4 Last?

Commercially available LiFePO4 batteries last anywhere from 2000 cycles to 10,000 cycles. The variance in this range is due to the many dependent factors for the cycle life. Users of the same capacity battery from the same brand often report different cycle life. The main reason for this is how your battery is kept and used.

There are also cycle life limitations based on the manufacturing end. Many manufacturers of non-branded batteries claim a very long cycle life. However, those batteries rarely live up to their lifespan, even when kept in pristine condition.

The 10,000 cycles is hardly the maximum ceiling on the LiFePO4 battery life. Many manufacturers claim their batteries will last for 20,000 cycles if kept as recommended.

An important thing to note is that cycle life is different from a battery lifespan. However, you can easily calculate how long your LiFePO4 battery will last.

What Factors Impact LiFePO4 Battery Life?

Many factors determine how many discharge cycles LiFePO4 battery will last. These factors are:

Battery Type

The cycle life is primarily dependent on the battery chemistry. Different types of batteries have different chemistries. Lead acid batteries do not work the same way as conventional lithium-ion batteries. Lithium ion batteries do not have the same chemistry as LiFePO4.

Here are some average cycle life values for different battery chemistries:

• Lead Acid Battery: 300 Cycles
• Nickel Cadmium Battery: 1000 Cycles
• Nickel Metal Hydride Battery: 400 Cycles
• Lithium Ion Battery (Cobalt): 1000 Cycles
• Lithium Ion Battery (Manganese): 1000 Cycles
• Lithium Iron Phosphate Battery: 3000 Cycles
• Eco Tree Lithium’s Lithium Iron Phosphate Battery: 5000 Cycles

There are two key takeaways from these reference cycle life values. First, any type of lithium battery outperforms lead-acid batteries by a huge margin. The second is about the performance of lithium-iron phosphate batteries. These batteries are the winners in terms of cycle life. Their average values are way over other lithium-based batteries. The real-life value is significantly higher than this average reference if the battery is cared for.

Depth of Discharge (DoD)

Manufacturers list a battery’s cycle life with a particular discharge depth. This is because the depth of discharge suggests the limit to which you should discharge your battery. You can discharge the battery lower, but it will only harm it.

Therefore, if the battery discharge cycles are going beyond its depth of discharge, the battery’s expected lifespan is lowered. This lowers its expected cycle life as well.

Charge Rate

Batteries come with a suggested charge rate and discharge rate. These values are expressed in terms such as 1C, 1.5C, etc. They represent the ideal current rate you should use when charging and discharging a battery. If the charge rate or discharge rate exceeds limit, the battery gets damaged. This lowers the expected cycle life as well.

Temperature

Higher temperatures accelerate the chemical reactions in the battery. This increases the battery capacity. However, the cycle life is reduced since the battery capacity depletes faster. The best cycle life is obtained when the battery is kept in the manufacturer’s recommended temperature range.

Usage Pattern

How the battery is used determines the cycle count the battery will last. Following practices like opportunity charging extend the battery’s cycle count even beyond the manufacturer’s listed value. Habits such as overcharging and over-discharging lower the cycle count significantly.

Build Quality

Build quality is something that users do not have any control over. Poor build qualities work and seem the same as top of the line options. However, with time the battery seals and parts begin to degrade. These parts are not replaceable or repairable. Therefore, you need to replace the entire battery. This means a lower cycle count than what you would otherwise expect.

How to Calculate the LiFePO4 Battery Cycle Life?

There is no accurate way of calculating the exact LiFePO4 cycle life. This is because of the several factors that cycle life depends on. However, you can get an idea of cycle life by calculating the battery runtime.

To calculate the runtime, you need to find the watt hours of the battery. This is done by multiplying the Ampere hour capacity of the battery with its rated voltage.

For instance, for a 100 Ah battery rated at 12V,

• Watt hours = Rated Voltage x Amp hour capacity
• Watt hours = 100x 12 = 1200 Wh

This value is then multiplied by the battery’s Depth of Discharge. Considering a depth of discharge of 80%,

• Usable Watt hours = DoD x Wh
• Usable Watt hours = 0.8 x 1200 = 960 Wh

To calculate battery runtime, you can divide the usable Wh with the applied load. Therefore, if you want to find the runtime when running a TV of 100 Watts,

• Runtime = Usable Watt hours / Applied Load in Watts
• Runtime = 960 Wh / 10 W = 9.6 hours

Tips to Optimise LiFePO4 Cycle Life

You can get a higher cycle count from these batteries by following a proper LiFePO4 maintenance protocol. Some tips to extend the cycle life of these batteries are:

• Getting manufacturer recommended battery charger eliminates the concern of worrying about charging rate. This can extend the life of Li-ion batteries without any extra effort.
• Many modern deep-cycle batteries come with a Battery Management System (BMS). This system has many protection and monitoring features to ensure the battery remains in optimal health. They provide a long cycle life to the battery without you having to monitor it manually.
• Different batteries have different Depth of Discharge (DoD) ratings. Follow the manufacturer provided rating for optimal results.
• Keep the battery in a safe working temperature. If the battery is outdoors, take appropriate steps to protect it from the sun.

Endnotes

The service life of LiFePO4 is one of the main reasons that attracts users towards this technology. If you are looking for a new battery, an LiFePO4 option by Eco Tree Lithium will surely last an upward of 5000 cycles. In fact, these batteries come with a 6-year warranty to show the manufacturer’s faith in these products. Browse through the Eco Tree Lithium catalogue to find the right battery for your requirements.

Frequently Asked Questions (FAQs)

Here are the answers to some common questions regarding LFP battery charge cycles and cycle life:

How many cycles is a lithium battery good for?

Good lithium batteries can last for more than 5000 cycles. This is true for the Lithium Iron Phosphate (LiFePO4) technologies. Conventional nickel or manganese based lithium batteries last for only 2000 cycles or so.

What is the 40-80 battery rule?

The 40-80 battery rule suggests keeping the battery State of Charge between 40% to 80%. This is done by charging the battery whenever it reaches 40% charge level. The charger is disconnected when the battery is charged to 80%. Following this rule extends the lifespan of the battery.