LiFePO4 battery is the best you can buy among any deep cycle batteries. However, there are countless options, even among LiFePO4 batteries. These batteries come in different voltages, ampere-hour ratings, features, and many other parameters. Therefore, you need to know how to choose a lifepo4 battery to buy the right one.
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This article will provide all the information you need on the subject. You will know about all the factors that play a role in buying decisions. You will also learn about the best places to get these batteries.
What is a LiFePO4 Battery?
LiFePO4 battery stands for Lithium Iron Phosphate batteries. They are named so because the cathode material is LiFePO4. The anode is made of graphite. LiFePO4 batteries are a considerable improvement over conventional lithium-ion batteries. Additionally, their performance is leaps and bounds ahead of lead-acid batteries. These reasons have made LiFePO4 the most popular battery choice in recent years.
Factors to Consider When Buying LiFePO4 Battery
Different users will have different preferences when buying a LiFePO4 battery. Your decision should be based on factors like:
The capacity of a battery represents how many appliances it can power and for how long. It is measured in Watt hours (Wh). The capacity is the primary factor to consider and the main factor that drives up the LiFePO4 battery cost.
Users often get confused when they cannot see a Wh rating mentioned on the battery. Instead, they find voltage and Amp hours (Ah) ratings.
That is alright. You can find the Wh rating by multiplying voltage and amp hours.
Wh = V x Ah
For a 12V battery with a 320 Ah rating, the Wh will be:
Wh = 12 x 320 = Wh
To find out how much capacity you need, you can add the wattage of all the appliances you use. Then you can multiply it by the hours you want to run them without charging the battery. This will give you the minimum watt hours of the lithium-ion batteries you should buy.
For instance, if you want to run a total of 300W load for 10 hours, you require a minimum of:
Minimum Wh = 300 x 10 = Wh
Since the load or running time can increase or decrease, the required battery should have more capacity than the minimum Watt hours you require. Therefore, the Wh battery will be a good fit for the Wh minimum capacity.
Many users focus on 'price' as the deciding factor. However, a better factor to consider should be the value for money of the battery.
Lead acid batteries are the cheaper option in the market today. However, their lifespan is only one-tenth that of a LiFePO4 battery. While LiFePO4 batteries can last over 10 years, a lead acid battery will run out after a year or so. Additionally, there is always the risk of cheaper batteries running out while on the job.
Therefore, opt for value for money instead of the price as the deciding factor. It can save you countless trouble in the long run. This brings us to our next important criterion.
It is essential to consider how many years a battery will last. You can save money and buy lead-acid batteries if you want a short fix for a few months. However, most users do not want that. Instead, they require a long-term solution.
A LiFePO4 battery is the best option in terms of battery life. A good quality LiFePO4 battery will easily last upward of 10 years. AGM and conventional lithium-ion batteries can work well for three to four years.
Cycle life means the number of charge and discharge cycle that your battery can undergo. A longer cycle life means a battery will last longer. Batteries do not come with a suggestive lifespan on the box. However, they do mention a cycle life. Choose an option with a longer cycle life for a better return on investment.
Warranty is a good indicator of the build quality of the battery and its lifespan. Lead acid batteries come with a 6-month warranty. Therefore, they are workable for up to a year until they demand replacement. LiFePO4 battery is a whole different game.
You will find different kinds of warranty periods with different LiFePO4 manufacturers. Eco Tree Lithium is the leader in the game as it provides a warranty of an astonishing 6-year. You can expect the Eco Tree Lithium batteries to easily work for over 10 years with a warranty like that.
Depth of Discharge (DoD) is a significant factor that makes people switch from existing lead acid batteries to lithium iron phosphate batteries. Depth of discharge denotes the usable capacity of the battery.
For instance, the depth of discharge for lead acid batteries is 50%. Therefore, you can use these batteries to 50% of their capacity. After that, they will require charging. However, for Eco Tree Lithium's LiFePO4 battery, the DoD is a whopping 100%. You can use LiFePO4 through the full rated capacity.
Here is an example for putting things in perspective. Suppose your capacity requirement is 200 Ah. You can meet this requirement with a 200 Ah LiFePO4 battery. However, you will need a 400 Ah battery capacity if opting for a lead acid battery due to its half depth of discharge.
Every battery has a distinct maintenance requirement. Lead acid batteries have many requirements like electrolyte top-ups and venting the buildup gases. Fortunately, maintenance of LiFePO4 battery is much simpler and easy.
Battery dimensions are important for applications like motorhomes. The battery compartments can accommodate a particular size battery bank. LiFePO4 battery has prefixed size groups to denote the standard size of the battery. Match the lithium battery group with your requirement.
Weight is not always on the priority list of important parameters. However, some users find having a lighter battery preferable. If that is the case, any lithium battery is a better buy over a lead acid battery. For instance, a lead acid battery pack of 500 Ah can weigh around 850 kg. The same job can be done by a 250 Ah lithium-ion battery weighing 210 kg. This means a considerable difference in weight.
The main differences come from the eliminated weight of lead plates and electrolytes. Additionally, lithium iron phosphate batteries have lighter electrodes.
Safety becomes essential when you operate your battery near life and property. There have been instances where lead acid battery leak fluids that cause corrosion of the battery and nearby appliances. Conventional lithium batteries have fire and explosion hazards with them. However, lithium iron phosphate batteries are made using very stable compounds of iron and phosphate. These will never explode or cause fire injury.
The voltage of the battery pack is important because it determines its usability. For instance, you cannot replace a 24V battery with a 48V battery and vice versa. Every type of voltage rating has a distinct application, advantage, and disadvantage. If you are replacing your old batteries, you will need to find old voltage rating and match new batteries with the same rating for a constant voltage.
Common voltage ratings are:
All batteries are known for performance stuttering in extreme temperatures. Freezing conditions can lead to battering running flat. These batteries often do not recover once the temperature toll takes place. Therefore, find the optimal temperature range of the battery. Better yet, choose Eco Tree Lithium batteries with an inbuilt heater for cold weather.
Modern batteries come with many features that add to the convenient user experience. Take the case of this battery. It has a Bluetooth feature to check your battery stats remotely. You do not have to open the battery compartment. You don't have to use a multimeter to check the voltage and current parameters. You can manage the battery remotely from a Bluetooth device.
Other secondary features can include LED indicators for the charging system. Having a handle to transport the battery is also a handy feature to have.
Always choose a LiFePO4 battery that comes with a BMS. A battery management system has a lot of safety protocols against potential hazards. All batteries are prone to irreversible overcharge and over-discharge damage. BMS protection measures cut off the circuit to eliminate any possibility of damage.
Modern energy technologies are pushing towards greener initiatives. It is recommended to choose an environmentally friendly battery option. For instance, cobalt-based batteries (like lithium cobalt oxide) are not environmentally friendly. This is because cobalt is rare and toxic in nature. LiFePO4 battery is one of the greenest battery out there.
Cobalt and lead come in toxic heavy metals category. These materials can cause health hazards if they come into human contact. Therefore, batteries that include these metals are considered unsafe. This includes all lead batteries. However, a lithium iron phosphate battery does not have any toxic substances in them.
Additionally, lead acid chemistry leads to the emission of toxic gases. You might be familiar with the pungent smell that often comes from lead batteries. Therefore, choose a battery that does not have any such risk. You will never need to vent lithium iron batteries because it releases no toxic gases.
Do You Need BMS in a LiFePO4 Battery?
Yes, you should always buy a LiFePO4 battery with a BMS. Lithium iron phosphate battery is a hefty investment. A BMS protects that investment from any harm. BMS will prolong the life of your battery significantly by monitoring every parameter.
Battery management systems come with surge protectors to avoid the harm of excessive currents. Additionally, many other circuits shield the battery from adverse situations. Many BMS also come with displays and relays that monitor data.
Where to Buy a LiFePO4 Battery?
Eco Tree Lithium is the best place to buy a lithium iron phosphate battery. These batteries outperform most batteries on the market. They have features like BMS, Bluetooth, an in-built heater, and a 6-year warranty. Additionally, you get the brand name of the leading LiFePO4 battery supplier globally.
You can easily choose the best battery with the above information. You can also differentiate between LiFePO4 and other lithium-ion batteries. A good battery can be the driving point for a decade of worry-free operation. A lousy option can lead to hazards, breakdowns, and chasing the manufacturer for a replacement. Therefore, spend extra time choosing the battery to avoid wasting your time later.
Frequently Asked Questions (FAQs)
Here are the answers to some common questions regarding LiFePO4 batteries:
No, all LiFePO4 batteries are not the same. The build quality of the batteries differs between manufacturers. These batteries also come in many different types, dimensions, capacity, voltage rating, and features.
Battery research is focusing on lithium chemistries so much that one could imagine that the battery future lies solely in lithium. There are good reasons to be optimistic as lithium-ion is, in many ways, superior to other chemistries. Applications are growing and are encroaching into markets that previously were solidly held by lead acid, such as standby and load leveling. Many satellites are also powered by Li-ion.
Lithium-ion has not yet fully matured and is still improving. Notable advancements have been made in longevity and safety while the capacity is increasing incrementally. Today, Li-ion meets the expectations of most consumer devices but applications for the EV need further development before this power source will become the accepted norm. BU-104c: The Octagon Battery ' What makes a Battery a Battery, describes the stringent requirements a battery must meet.
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As battery care-giver, you have choices in how to prolong battery life. Each battery system has unique needs in terms of charging speed, depth of discharge, loading and exposure to adverse temperature. Check what causes capacity loss, how does rising internal resistance affect performance, what does elevated self-discharge do and how low can a battery be discharged? You may also be interested in the fundamentals of battery testing.
The lithium-ion battery works on ion movement between the positive and negative electrodes. In theory such a mechanism should work forever, but cycling, elevated temperature and aging decrease the performance over time. Manufacturers take a conservative approach and specify the life of Li-ion in most consumer products as being between 300 and 500 discharge/charge cycles.
In , small wearable batteries deliver about 300 cycles whereas modern smartphones have a cycle life requirement is 800 cycles and more. The largest advancements are made in EV batteries with talk about the one-million-mile battery representing 5,000 cycles.
Evaluating battery life on counting cycles is not conclusive because a discharge may vary in depth and there are no clearly defined standards of what constitutes a cycle(See BU-501: Basics About Discharging). In lieu of cycle count, some device manufacturers suggest battery replacement on a date stamp, but this method does not take usage into account. A battery may fail within the allotted time due to heavy use or unfavorable temperature conditions; however, most packs last considerably longer than what the stamp indicates.
The performance of a battery is measured in capacity, a leading health indicator. Internal resistance and self-discharge also play roles, but these are less significant in predicting the end of battery life with modern Li-ion.
Figure 1 illustrates the capacity drop of 11 Li-polymer batteries that have been cycled at a Cadex laboratory. The 1,500mAh pouch cells for mobile phones were first charged at a current of 1,500mA (1C) to 4.20V/cell and then allowed to saturate to 0.05C (75mA) as part of the full charge saturation. The batteries were then discharged at 1,500mA to 3.0V/cell, and the cycle was repeated. The expected capacity loss of Li-ion batteries was uniform over the delivered 250 cycles and the batteries performed as expected.
Eleven new Li-ion were tested on a Cadex C battery analyzer. All packs started at a capacity of 88'94% and decreased to 73'84% after 250 full discharge cycles. The mAh pouch packs are used in mobile phones.
Although a battery should deliver 100 percent capacity during the first year of service, it is common to see lower than specified capacities, and shelf life may contribute to this loss. In addition, manufacturers tend to overrate their batteries, knowing that very few users will do spot-checks and complain if low. Not having to match single cells in mobile phones and tablets, as is required in multi-cell packs, opens the floodgates for a much broader performance acceptance. Cells with lower capacities may slip through cracks without the consumer knowing.
Similar to a mechanical device that wears out faster with heavy use, the depth of discharge (DoD) determines the cycle count of the battery. The smaller the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses. Partial discharge on Li-ion is fine. There is no memory and the battery does not need periodic full discharge cycles to prolong life. The exception may be a periodic calibration of the fuel gauge on a smart battery or intelligent device(See BU-603: How to Calibrate a 'Smart' Battery)
The following tables indicate stress related capacity losses on cobalt-based lithium-ion. The voltages of lithium iron phosphate and lithium titanate are lower and do not apply to the voltage references given.
Note:
Tables 2, 3 and 4 indicate general aging trends of common cobalt-based Li-ion batteries on depth-of-discharge, temperature and charge levels, Table 6 further looks at capacity loss when operating within given and discharge bandwidths. The tables do not address ultra-fast charging and high load discharges that will shorten battery life. No all batteries behave the same.Table 2 estimates the number of discharge/charge cycles Li-ion can deliver at various DoD levels before the battery capacity drops to 70 percent. DoD constitutes a full charge followed by a discharge to the indicated state-of-charge (SoC) level in the table.
Depth of Discharge
Discharge cycles
NMC
LiPO4
100% DoD
~300
~600
80% DoD
~400
~900
60% DoD
~600
~1,500
40% DoD
~1,000
~3,000
20% DoD
~2,000
~9,000
10% DoD
~6,000
~15,000
Table 2: Cycle life as a function ofdepth of discharge** 100% DoD is a full cycle; 10% is very brief. Cycling in mid-state-of-charge would have best longevity.
Lithium-ion suffers from stress when exposed to heat, so does keeping a cell at a high charge voltage. A battery dwelling above 30°C (86°F) is considered elevated temperature and for most Li-ion a voltage above 4.10V/cell is deemed as high voltage. Exposing the battery to high temperature and dwelling in a full state-of-charge for an extended time can be more stressful than cycling. Table 3 demonstrates capacity loss as a function of temperature and SoC.
Most Li-ions charge to 4.20V/cell, and every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life. For example, a lithium-ion cell charged to 4.20V/cell typically delivers 300'500 cycles. If charged to only 4.10V/cell, the life can be prolonged to 600'1,000 cycles; 4.0V/cell should deliver 1,200'2,000 and 3.90V/cell should provide 2,400'4,000 cycles.
On the negative side, a lower peak charge voltage reduces the capacity the battery stores. As a simple guideline, every 70mV reduction in charge voltage lowers the overall capacity by 10 percent. Applying the peak charge voltage on a subsequent charge will restore the full capacity.
In terms of longevity, the optimal charge voltage is 3.92V/cell. Battery experts believe that this threshold eliminates all voltage-related stresses; going lower may not gain further benefits but induce other symptoms(See BU-808b: What causes Li-ion to die?) Table 4 summarizes the capacity as a function of charge levels. (All values are estimated; Energy Cells with higher voltage thresholds may deviate.)
Every 0.10V drop below 4.20V/cell doubles the cycle but holds less capacity. Raising the voltage above 4.20V/cell would shorten the life. The readings reflect regular Li-ion charging to 4.20V/cell.
Guideline: Every 70mV drop in charge voltage lowers the usable capacity by about 10%.
Note: Partial charging negates the benefit of Li-ion in terms of high specific energy.
* Similar life cycles apply for batteries with different voltage levels on full charge.
** Based on a new battery with 100% capacity when charged to the full voltage.
Experiment: Chalmers University of Technology, Sweden, reports that using a reduced charge level of 50% SOC increases the lifetime expectancy of the vehicle Li-ion battery by 44'130%.
Most chargers for mobile phones, laptops, tablets and digital cameras charge Li-ion to 4.20V/cell. This allows maximum capacity, because the consumer wants nothing less than optimal runtime. Industry, on the other hand, is more concerned about longevity and may choose lower voltage thresholds. Satellites and electric vehicles are such examples.
For safety reasons, many lithium-ions cannot exceed 4.20V/cell. (Some NMC are the exception.) While a higher voltage boosts capacity, exceeding the voltage shortens service life and compromises safety. Figure 5 demonstrates cycle count as a function of charge voltage. At 4.35V, the cycle count of a regular Li-ion is cut in half.
Besides selecting the best-suited voltage thresholds for a given application, a regular Li-ion should not remain at the high-voltage ceiling of 4.20V/cell for an extended time. The Li-ion charger turns off the charge current and the battery voltage reverts to a more natural level. This is like relaxing the muscles after a strenuous exercise(See BU-409: Charging Lithium-ion)
Figure 6 illustrates dynamic stress tests (DST) reflecting capacity loss when cycling Li-ion at various charge and discharge bandwidths. The largest capacity loss occurs when discharging a fully charged Li-ion to 25 percent SoC (black); the loss would be higher if fully discharged. Cycling between 85 and 25 percent (green) provides a longer service life than charging to 100 percent and discharging to 50 percent (dark blue). The smallest capacity loss is attained by charging Li-ion to 75 percent and discharging to 65 percent. This, however, does not fully utilize the battery. High voltages and exposure to elevated temperature is said to degrade the battery quicker than cycling under normal condition. (Nissan Leaf case)
* Discrepancies exist between Table 2 and Figure 6 on cycle count. No clear explanations are available other than assuming differences in battery quality and test methods. Variances between low-cost consumer and durable industrial grades may also play a role. Capacity retention will decline more rapidly at elevated temperatures than at 20ºC.
Only a full cycle provides the specified energy of a battery. With a modern Energy Cell, this is about 250Wh/kg, but the cycle life will be compromised. All being linear, the life-prolonging mid-range of 85-25 percent reduces the energy to 60 percent and this equates to moderating the specific energy density from 250Wh/kg to 150Wh/kg. Mobile phones are consumer goods that utilize the full energy of a battery. Industrial devices, such as the EV, typically limit the charge to 85% and discharge to 25%, or 60 percent energy usability, to prolong battery life(See Why Mobile Batteries do not last as long as an EV Battery)
Increasing the cycle depth also raises the internal resistance of the Li-ion cell. Figure 7 illustrates a sharp rise at a cycle depth of 61 percent measured with the DC resistance method(See also BU-802a: How does Rising Internal Resistance affect Performance?) The resistance increase is permanent.
Figure 7: Sharp rise in internal resistance by increasing cycle depth of Li-ion [4]Note: DC method delivers different internal resistance readings than with the AC method (green frame). For best results, use the DC method to calculate loading.
Figure 8 extrapolates the data from Figure 6 to expand the predicted cycle life of Li-ion by using an extrapolation program that assumes linear decay of battery capacity with progressive cycling. If this were true, then a Li-ion battery cycled within 75%'25% SoC (blue) would fade to 74% capacity after 14,000 cycles. If this battery were charged to 85% with same depth-of-discharge (green), the capacity would drop to 64% at 14,000 cycles, and with a 100% charge with same DoD (black), the capacity would drop to 48%. For unknown reasons, real-life expectancy tends to be lower than in simulated modeling(See BU-208: Cycling Performance)
Li-ion batteries are charged to three different SoC levels and the cycle life modelled. Limiting the charge range prolongs battery life but decreases energy delivered. This reflects in increased weight and higher initial cost.
Battery manufacturers often specify the cycle life of a battery with an 80 DoD. This is practical because batteries should retain some reserve before charge under normal use(See BU-501: Basics about Discharging, 'What Constitutes a Discharge Cycle') The cycle count on DST (dynamic stress test) differs with battery type, charge time, loading protocol and operating temperature. Lab tests often get numbers that are not attainable in the field.
Environmental conditions, not cycling alone, govern the longevity of lithium-ion batteries. The worst situation is keeping a fully charged battery at elevated temperatures. Battery packs do not die suddenly, but the runtime gradually shortens as the capacity fades.
Lower charge voltages prolong battery life and electric vehicles and satellites take advantage of this. Similar provisions could also be made for consumer devices, but these are seldom offered; planned obsolescence takes care of this.
A laptop battery could be prolonged by lowering the charge voltage when connected to the AC grid. To make this feature user-friendly, a device should feature a 'Long Life' mode that keeps the battery at 4.05V/cell and offers a SoC of about 80 percent. One hour before traveling, the user requests the 'Full Capacity' mode to bring the charge to 4.20V/cell.
The question is asked, 'Should I disconnect my laptop from the power grid when not in use?' Under normal circumstances this should not be necessary because charging stops when the Li-ion battery is full. A topping charge is only applied when the battery voltage drops to a certain level. Most users do not remove the AC power, and this practice is safe.
Modern laptops run cooler than older models and reported fires are fewer. Always keep the airflow unobstructed when running electric devices with air-cooling on a bed or pillow. A cool laptop extends battery life and safeguards the internal components. Energy Cells, which most consumer products have, should be charged at 1C or less. Avoid so-called ultra-fast chargers that claim to fully charge Li-ion in less than one hour.
[1] Courtesy of Cadex
[2] Source: Choi et al. ()
[3] B. Xu, A. Oudalov, A. Ulbig, G. Andersson and D. Kirschen, "Modeling of Lithium-Ion Battery Degradation for Cell Life Assessment," June . [Online]. Available: https://www.researchgate.net/publication/_Modeling_of_Lithium-Ion_Battery_Degradation_for_Cell_Life_Assessment.
[4] Source: Technische Universität München (TUM)
[5] With permission to use. Interpolation/extrapolation by OriginLab.
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