One of the things you'll consider when buying a battery-powered device is the battery life. The battery can only last as long as its charge cycles. Some batteries have more charge cycles, lasting longer than others.
The charge cycle is the process of fully charging a device battery and then discharging it close to zero per cent. As the charge cycles are depleted, the battery degrades, and eventually, your device will need a new battery.
We’ll explore how many charge cycles different battery technologies have before degrading and becoming inefficient. You’ll also know the best battery technologies for different devices.
Lithium-Ion (Li-Ion) Batteries Charge Cycle
Mobile devices like smartphones and laptops use lithium-ion batteries. At the same time, electric vehicles also use this battery technology. You’ll also find this battery type in home energy storage solutions.
These batteries pack more energy in a small space and are incredibly lightweight. They also boast one of the best lifespans. The charge cycles depend on a few factors, but they average 500 – 1,000 cycles.
Charging Phase
Lithium-ion battery charges in two stages. For most of the charging of your battery, constant current forces lithium ions to move to the anode electrode from the cathode. The battery stores the migrating ions in the graphite layer. Each battery cell will attain 4.2V.
The second charging stage occurs when individual battery cells have attained the voltage threshold (4.2V per cell). Now, the charger supplies a constant voltage to the battery while gradually reducing the electric current supply.
Discharge Phase
Your battery discharges while in use. Lithium ions return to the cathode electrode, causing the battery to supply an electric current. As a device draws current from the battery, the voltage plummets.
Lithium Iron Phosphate (LiFePO4) Batteries
These batteries are more potent than Li-ion batteries. You can expect them to supply energy to more powerful devices and tools, like electric vehicles and power tools. You’ll also find them in home energy storage solutions.
LiFePO4 batteries boast an impressive charge cycle of 2,000 – 5,000. However, Lithium iron phosphate batteries have a lower energy density. As such, they’re not as compact as Li-ion batteries.
LiFePO4 Charging Phase
Like its counterpart, the Li-ion battery, this battery technology uses two charging stages. The constant current charging stage occurs first. Your battery charge supplies a continuous current to your battery until individual cells attain 3.65V.
Your battery will use this charging stage until it is 90% complete. Then, your charger provides constant volts to complete the charging phase. The current supplied by the charger gradually reduces in the second stage.
Lithium ions move to the anode through an electrolyte. At the same time, electrons travel to the anode through an external circuit. The ions are stored in the anode structure.
Discharging LiFePO4 Battery
The discharge process is the reverse of the charging process. Lithium ions return to the cathode while electrons flow externally to power a connected device. As ions re-insert into the cathode material structure, they release energy.
Lead-Acid Batteries
These batteries have fewer charge cycles of 300 – 500. The automotive industry and power backup systems use Lead-Acid batteries for power. You’ll likely use this battery for solar energy storage. This battery technology uses three charging stages.
Bulk Charging
The battery relies on this stage for up to 80% of charge time. Your battery charger supplies maximum current at a constant flow until individual cells attain 14.4V. The battery charges rapidly in this phase.
Absorption Charging
Your battery now draws constant voltage from its charger at this stage. The current supplied gradually plummets as the charge completes the remaining 20% charge capacity. This stage is essential to prevent overcharging, which can reduce battery life.
Float Charging
The battery reduces the voltage rating in individual cells to 13.2 – 13.8 to prevent overcharging. At this charging stage, your lead-acid battery is ready for backup power.
Lead-Acid Battery Discharge
Lead reacts with the sulphuric acid to form lead sulfate, releasing electrons that generate electricity. Battery voltage gradually drops as a connected device draws energy from your lead-acid battery.
Nickel-Cadmium (NiCd) Batteries
You can expect to charge your NiCd battery 500 – 1,000 times before it loses efficiency. What’s incredible about this battery is that it can supply short bursts of high current. It also performs incredibly well in extreme temperatures, making it a preferred choice for aviation and medical equipment.
However, they have environmental concerns because of toxic cadmium content. They also have poor memory and can lose efficiency if you don’t fully discharge them before a recharge.
Charging Phase
The battery boasts a fast charge capability since you can charge this battery to full capacity in 2 – 1 hour. Your battery’s temperature will increase when charging it, which is how your charger knows when to terminate charging.
At the same time, the charger tracks voltage drops to stop charging the battery. If your battery is fully charged, the charger provides optimal maintenance charge or low trickle charge to replace energy lost due to self-discharge.
Discharge Phase
You can discharge this battery fully without any immediate risk of damage. However, you want to discharge it fully periodically to prevent the memory effect. Your connected devices will draw steady voltage from this battery, making it one of the most reliable alternative power sources.
Why Charge Cycles Differ Across Battery Technologies
Batteries have different charge cycles because they use different charging phases tailored to their chemical technology. For example, lithium-ion batteries charge using a chemical reaction different from a lead-acid battery reaction.
Additionally, the charge cycle depends on the battery's structural and operational factors. As you've already seen, some batteries have more charge cycles before their energy storage capacity plummets.
Battery Chemistry and Electrochemical Stability
Lithium-ion batteries experienced decreased performance after 500 – 1,000 charge cycles. These batteries have a higher energy density. However, they degrade faster than LiFePO4 due to more electrode stress.
On the other hand, LiFePO4 batteries degrade after 2,000 – 5,000 charge cycles. They boast a highly stable crystal structure that lasts longer than Li-ion batteries.
Lead-acid batteries can last 300 – 1,000 charge cycles, depending on depth of charge. However, they degrade due to sulfation and water loss.
Nickel-cadmium batteries have the third-best lifespan, lasting from 1,000 to 1,500 cycles. While this battery doesn't degrade like other types, it suffers from a memory effect.
Depth of Charge and Cycle Stress
The number of times you fully charge and discharge a battery also depends on the depth of charge. If a battery was 100% full and now it's 40% full, the depth of discharge is 60%. Think of the depth of discharge as the amount of energy a device has drawn from your battery.
Batteries usually experience stress during the charging phase. The longer the charging phase lasts, the more stress you put on the battery's chemical structure. Therefore, a deeper depth of discharge causes more stress and degrades the battery faster.
Ideal depth of charge for batteries:
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Lithium-ion batteries: 80%
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Lithium iron phosphate batteries: 80 – 90%
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Lead acid batteries: 50%. But you can occasionally discharge to 80%
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Nickel Cadmium batteries: 20 – 30% to extend the battery life.
Exceeding the depth of discharge (DoD) stresses your battery, cutting its lifespan short. If your battery has to recharge from a fresh start, you deplete charge cycles fast.
Structural Changes in Battery
Batteries also experienced reduced energy capacity over time due to changes in the electrode structures. Lithium-ion and Lithium-iron phosphate batteries experience structural changes due to lithium plating. At the same time, the cathode electrode suffers from cathode cracking.
On the other hand, lead acid batteries experience sulfation that causes structural changes on their electrodes. As a result, they don't provide sufficient power, and the battery becomes less efficient.
You'll also experience a memory effect with your NiCd batteries, causing them to generate less electrical power. A change in electrode structure also stresses the battery's internal components, reducing the life expectancy of your power storage solution.
Temperature Sensitivity
Heat can reduce the charge cycles of a battery as it causes battery wear. Heat will make your battery's internal components reduce electrical conductivity and break down the electrolyte. Batteries with lithium ions are specifically more sensitive to heat.
However, Lithium iron phosphate batteries handle heat better. The same can be said about Nickel Cadmium (NiCd) batteries. Your Li-ion battery can handle 40°C or lower. On the other hand, LiFePO4 batteries can handle 60°C.
Lead-acid batteries can withstand moderate heat. However, they lose water, which can reduce the charge cycles. NiCd batteries can handle extreme temperatures better than the two battery types.
Charging and Discharging Effects
Batteries build up heat during charging and discharging. However, the amount of heat build-up varies depending on the battery technology. Li-ion and LiFePO4 batteries build up less heat and can perform incredibly well for many charge cycles.
On the other hand, lead-acid batteries create more heat during the charging phase, making them degrade faster. As heat builds up, batteries' efficiency reduces. Li-ion batteries are 90–95% efficient, and LiFePO4 boasts a 95–98% efficiency.
NiCd batteries have an efficiency of 70–90%, while lead acid batteries have 75–85%. Managing external heat sources can boost charge cycles. Therefore, keep charging batteries under ideal conditions to improve their lifespan.
Final Verdict
A battery’s charge cycle varies depending on the battery technology. Lithium-ion phosphate batteries tend to have more charge cycles than other battery types. However, all batteries eventually run out of charge cycles, especially with deeper depth of discharge. Therefore, you want to keep your battery within the ideal depth of discharge to extend their lifespan.
