Sep. 08, 2025
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.
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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.
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.
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.
* 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.
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.
Now the market is full of lithium battery of various sizes and brands, and many users are trying them out with a trial mentality. However, some users report that the effect of the battery is not satisfactory. Next, We will tell you how to choose the battery correctly, and teach you a few ways to judge the quality of the battery. Selecting the right battery cells for your device can ensure that it operates effectively and safely.
Before you purchase a battery for your device, it’s important to understand your device’s battery requirements.
The manual or website for your device should provide information on the recommended or required battery type, size, and capacity for your device. For example, if you’re looking to replace the battery in your cell , the manual may indicate that the device requires a lithium-ion battery with a specific voltage and capacity.
Power consumption is a crucial factor to consider when selecting a battery for your device. Look at the device’s power consumption and calculate how long you want the battery to last. This can help you determine the required capacity of the battery. For example, if you’re using a flashlight for an extended period, you’ll need a battery with a high capacity to ensure it lasts for the duration of your use.
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Make sure the battery’s voltage output matches the device’s requirements. Using a battery with a different voltage can damage the device or cause it to malfunction. For example, if your device requires a 3.7-volt battery, using a battery with a higher voltage can cause overheating or damage to the device’s circuits.
Some devices have limited space for a battery or have weight limitations, so it’s important to select a battery that fits within these limitations. For example, if you’re looking for a battery for a drone, you’ll need to consider the weight of the battery, as it can impact the drone’s flight time and stability.
There are various battery types available, each with their pros and cons. Lithium-ion batteries are commonly used in electronic devices due to their high capacity, low self-discharge rate, and light weight. Alkaline batteries are commonly used in low-power devices such as remote controls and flashlights. NiMH batteries are rechargeable and commonly used in high-power devices such as digital cameras. By comparing the pros and cons of each type, you can select the best battery for your device.
After clearly understanding your device or your design, we need to learn how to judge the quality of lithium batteries.
Some people think that the key indicator of the battery is the service life of the battery, but all indicators need to be based on the premise of safety. If there is no safety guarantee in the application of lithium battery, then for us, it is equivalent to a threat to life.
When purchasing a battery, check whether the lithium battery has a circuit protection board(PCB). The characteristics of the lithium battery determine that it must be equipped with a protection board to avoid overcharging, over discharge, short circuit, etc. of the lithium battery.
If there is no protective plate, the biggest danger of this kind of battery is deformation, explosion and leakage. Although with technology get better and some lithium batteries will not catch fire and make big explosion, some potential problems still exist which will decrease the service time of lithium batteries such as short circuit, over discharge and over charge and so on. In addition, rechargeable lithium battery packs without protective plates are also vulnerable to the influence of the external environment.For example, when the temperature is too high or too low, the performance and life of the battery pack will be affected to varying degrees.The protection board can improve the stability and safety of the battery pack by controlling the charging and discharging process of the battery pack.
According to the current batteries on the market (lead-acid batteries, lithium batteries, LiFePO4 batteries, Li-PO batteries), LiFePO4 batteries maybe are safer and do not deflagrate easily.
Different capacity, power, and last time will directly lead to a large difference in the price of electric vehicles.
At present, the more common lithium batteries are 12V 20Ah, 24V 30Ah, 48V 40Ah and other different sizes. Not only denpend on common size , but also depends on whether the capacity of the battery is accurately marked. If it is not marked, it is likely to be an inferior battery.
Why?
This kind of battery may be reassembled from inferior batteries or recycled battery cells. Don’t blindly pursue low prices. This kind of battery has a short life and unstable performance. If it is used improperly, it is very likely to damage the equipment. Oh, for example: Catching Fire.
The battery capacity will gradually decrease as it is used for a longer period of time, and the range of electric vehicles will become shorter and shorter. Therefore, if you want a longer service life, choose one with a larger battery capacity. Of course, you need a little more budget.
The safety hazards of lithium batteries are also related to the internal pressure, structure, process design and other reasons of the battery. When we want to judge the quality of lithium batteries, it mainly depends on the workmanship, size and craftsmanship. For batteries with the same capacity, lithium-ion batteries feel lighter than nickel-metal hydride batteries and nickel-cadmium batteries.
After observising the lithium battery, we can touch then. In general, we need to judge whether the seams of the battery shell are tight or not, and whether there are burrs or oil stains or not.
From this aspect, it can also be indirectly inferred whether the battery is prone to leakage.
The cycle life refers to the number of repeated charges and discharges that the battery can experience, and the charge and discharge conditions have a great impact on it. The greater the charging current (the faster the charging speed), the shorter the cycle life; the deeper the discharge depth, the shorter the battery life.According to the newly formulated electric vehicle battery standard, the life of the battery is expressed by the number of charge and discharge cycles of a certain capacity of 70%, and the qualified bottom line is 500 times.
Sometimes people find it strange that the electric car is obviously fully charged. Why is the battery dead after being left there for a period of time without riding?
In fact, this is due to the self-discharge rate of the lithium battery. Normally, when we store our lithium batteries correctly, the stored capacity will drop around 0.5 to 3% per month. If the reduced value exceeds the range, then the battery is not normal.
Examples of applying these considerations:
1. CELL BATTERY REPLACEMENT
Let’s say you have a Samsung Galaxy S21 that requires a mAh battery with a voltage of 3.85V. The battery capacity is measured in milliampere-hours (mAh), and it indicates the amount of charge the battery can hold. The voltage specifies the electric potential difference between the positive and negative terminals of the battery.
To calculate the wattage of the battery, you can use the formula: Wattage = Voltage x Current. In this case, the wattage of the battery would be 15.4 watts (3.85V x 4A). This calculation helps you determine how much power the battery can deliver to your device.
2.FLASHLIGHT BATTERY SELECTION:
Let’s say you have a flashlight that requires a battery with a voltage of 3.7V and a capacity of mAh. The flashlight’s power consumption is 6 watts, and you want the battery to last for at least 4 hours.
To determine the required capacity of the battery, you can use the formula: Capacity (in Ah) = Power (in watts) x Time (in hours) / Voltage (in volts). In this case, the required capacity of the battery would be 0.648 Ah (6W x 4h / 3.7V). You would need a battery with a capacity of at least 648 mAh to power the flashlight for 4 hours.
To calculate the wattage of the battery, you can use the formula: Wattage = Voltage x Current. In this case, the wattage of the battery would be 11.1 watts (3.7V x 3A). This calculation helps you determine how much power the battery can deliver to your device.
3. DRONE BATTERY SELECTION:
Let’s say you have a DJI Mavic Air 2 drone that requires a battery with a voltage of 11.55V and a capacity of mAh. The drone’s weight is 570 grams, and you want the battery to last for at least 30 minutes.
To determine the required capacity of the battery, you can use the formula: Capacity (in Ah) = Power (in watts) x Time (in hours) / Voltage (in volts). In this case, the required capacity of the battery would be 1.91 Ah (123.75W x 0.5h / 11.55V). You would need a battery with a capacity of at least mAh to power the drone for 30 minutes.
To calculate the wattage of the battery, you can use the formula: Wattage = Voltage x Current. In this case, the wattage of the battery would be 40.425 watts (11.55V x 3.5A). This calculation helps you determine how much power the battery can deliver to your device.
4.BOAT BATTERY SELECTION:
Let’s say you have a 24-volt trolling motor on your boat that requires two 12-volt batteries. The motor draws a maximum current of 30 amps and you want the batteries to last for at least 6 hours.
To determine the required capacity of each battery, you can use the formula: Capacity (in Ah) = Current (in amps) x Time (in hours). In this case, the required capacity of each battery would be 180 Ah (30A x 6h / 2). You would need two batteries with a capacity of at least 180 Ah each to power the trolling motor for 6 hours.
To determine the required capacity of each battery in watt-hours, you can use the formula: Capacity (in Wh) = Voltage (in V) x Capacity (in Ah). In this case, the required capacity of each battery would be 2,160 Wh (12V x 180 Ah). You would need two batteries with a capacity of at least 2,160 Wh each to power the trolling motor for 6 hours.
To calculate the wattage of each battery, you can use the formula: Wattage = Voltage x Current. In this case, the wattage of each battery would be 360 watts (12V x 30A). This calculation helps you determine how much power the battery can deliver to your device.
5. RC BATTERY SELECTION:
Let’s say you have a high-performance RC car that requires a LiPo (Lithium Polymer) battery with a voltage of 14.8V and a capacity of mAh. The car draws a maximum current of 60 amps, and you want the battery to provide maximum power output.
To determine the required capacity of the battery, you can use the formula: Capacity (in Ah) = Current (in amps) x Time (in minutes) / 60. In this case, the required capacity of the battery would be 50 Ah (60A x 5 min / 60). You would need a LiPo battery with a capacity of at least 50 Ah to power the RC car.
To calculate the wattage of the battery, you can use the formula: Wattage = Voltage x Current. In this case, the wattage of the battery would be 888 watts (14.8V x 60A). This calculation helps you determine how much power the battery can deliver to your device.
In conclusion, When choosing the right battery for your device, it’s important to consider factors like capacity, voltage, size, weight, and cost. By understanding the specifications and performance of these popular battery types, you can make an informed decision and ensure optimal performance for your electronic devices.
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