Temperature Characteristics:Since the migration rate of rechargeable batteries in electrolyte fluid and electrode sheets is closely related to temperature, fluctuations in temperature can significantly affect the technical performance of the batteries.
Storage Temperature:Generally speaking, due to the presence of liquid inside, long-term storage at low temperatures can damage the internal chemicals of the battery. Therefore, it is recommended to store them at temperatures no lower than -20°C when possible. Likewise, excessively high temperatures also prevent the battery from achieving its rated capacity, so the storage temperature should generally not exceed 40°C. The normal storage temperature range for rechargeable batteries is -20°C to +65°C. When the temperature drops below -20°C, the electrolyte inside the battery will solidify, making the internal resistance infinitely large and rendering the battery unusable. When the temperature exceeds +65°C, side reactions may occur in the electrolyte, producing large amounts of gas, and the resin adhesive in the electrode sheets may also degrade, leading to gradual aging and decline of the entire battery, or even short-term failure.
Charging Temperature:In general, the charging temperature range is 0°C to 45°C.
Discharge Temperature:In general, the discharge temperature range is -20°C to 65°C; however, in some special cases, low-temperature or high-temperature batteries may be used.
Battery packs are usually discharged before leaving the factory to prevent short circuits caused by shaking or other factors during transportation. Typically, new batteries come without charge or only contain around 20% of their capacity.
New batteries or those that have not been used for a long time may not have their active materials fully activated. Before use, they usually require two or three cycles of small-current (0.1C) charge and discharge to reach their nominal capacity.
Batteries that will not be used for a long time should be stored in a charged state. It is generally advisable to pre-charge them to 50%–100% capacity before storage. It is recommended to recharge them once every three months to restore them to full saturation.
Battery Usage Precautions:
Do not burn or disassemble batteries, as the chemicals inside are corrosive and can harm skin and eyes.
Do not pull on the battery leads or plugs to avoid damaging solder joints or connection points.
Do not mix batteries of different models.
When welding batteries of different models, use connecting pieces or similar methods.
Before first use, charge the battery fully with a small current.
Do not charge batteries in parallel, as this may produce irregular charging currents.
Do not use batteries in reverse or cause them to short-circuit.
After a battery has been fully discharged, extend the charging time to achieve full saturation.
Store batteries in a cool, ventilated, and dry environment with temperatures not exceeding 45°C.
Do not store large quantities of batteries densely together when they are fully or half-charged.
Do not expose batteries to acidic gases or place them near sources of fire.
Primary Batteries:Refers to batteries that cannot be recharged and are for single-use discharge only. However, primary batteries typically have greater capacity than rechargeable batteries of the same specifications, such as zinc-manganese, alkaline dry batteries, lithium coin cells, and lithium thionyl chloride batteries.
Secondary batteries:Refers to batteries that can be repeatedly charged and recycled, such as lead-acid, nickel-cadmium, nickel-metal hydride, lithium-ion, lithium-polymer, fuel, zinc, aluminum, and magnesium-air batteries.
Rated capacity: Refers to the amount of electrical energy a battery can release when discharged from a fully charged state to the cut-off voltage under no-load conditions, generally expressed in mAh or Ah (1Ah = 1000mAh). However, when the battery is connected to a load during use and over time, the amount of electricity released will decrease. Since charging and discharging occur under certain C-rate conditions, the battery’s capacity is directly related to the C-rate. Typically, the nominal capacity of a battery refers to the capacity tested at a 0.2C rate. The higher the C-rate, the lower the discharge rate. Charging capacity (Ah or mAh) = charging current × charging time; discharging capacity (Ah or mAh) = discharging current × discharging time. Generally speaking, discharging at 0.2C current can achieve about 95%–100% of the discharge rate, while discharging at 1C current can only reach about 90% of the discharge rate. Due to the influence of the battery's raw material characteristics on charging, it usually requires about 120%–160% more time than the equivalent current discharge time. For example, an NI-MH AA 1800mAh battery takes about 6–8 hours to charge at 0.2C (360mA), while it can discharge for about 5 hours at 0.2C (360mA).
Rated voltage:Refers to the potential difference caused by the chemical reaction between the positive and negative electrode materials of the battery, resulting in this voltage value. Different batteries produce different voltages due to their different positive and negative electrode materials, such as lead-acid: 2V per cell, nickel-cadmium and nickel-metal hydride: 1.2V per cell, lithium-ion batteries: 3.6V per cell. Additionally, battery voltage continuously rises to a certain value during charging and continuously drops to a certain value during discharging.
Open-circuit voltage:Refers to the voltage of the battery when it is not connected to an external circuit or load. The open-circuit voltage has a certain relationship with the remaining energy of the battery, which is why mobile phone battery indicators are designed based on this principle.
Internal resistance:Refers to the impedance naturally generated within the battery by its chemical materials. Generally speaking, the smaller the internal resistance, the better the battery’s charge and discharge performance. Battery internal resistance is a very complex yet very important characteristic, also known as battery impedance, and includes DC resistance and AC resistance. Factors affecting battery internal resistance include: ① the composition of the electrolyte; ② the formulation of the materials in the positive and negative electrode plates, such as the content of conductive carbon powder; ③ the geometric area and specific surface area of the positive and negative electrode plates; ④ the metal substrate (copper foil and aluminum foil); ⑤ the interface state between the electrolyte and the positive and negative electrode plates; ⑥ temperature; ⑦ the charging state (open-circuit voltage of the battery); ⑧ the measurement frequency; ⑨ the internal structural design of the battery.
C: Used to indicate the ratio of the current magnitude during battery charging and discharging, i.e., the rate. For example, for a 1200mAh battery, 0.2C means 240mA (0.2 times 1200mAh), and 1C means 1200mA (1 times 1200mAh). Charging and discharging efficiency is also related to C (rate). At a 0.2C rate, the charging and discharging efficiency of polymer lithium batteries should be around 99.8%. Charging and discharging efficiency = discharging capacity / charging capacity × 100%
Discharge cut-off voltage:Refers to the voltage reached when a fully charged battery is discharged until it is depleted (further discharge would constitute over-discharge, which can severely damage the battery’s lifespan and performance). Generally speaking, for lead-acid batteries: 1.8V per cell, nickel-cadmium and nickel-metal hydride: 1.0V per cell, lithium-ion batteries: 2.75V per cell.
Open-circuit voltage:Refers to the voltage between the positive and negative terminals of the battery when it is not under load.
Depth of discharge:The ratio of the amount of electricity discharged compared to the rated capacity of the battery.
Overcharging (or overdischarging):Refers to exceeding the specified charging (or discharging) state of the battery. Further charging (or discharging) may cause battery leakage or degradation.
Energy density:Refers to the amount of energy released per unit volume or per unit mass, typically expressed as volumetric energy density (Wh/L) and gravimetric energy density (Wh/kg).
Self-discharge:After a battery is fully charged, if it is left without contact with an external circuit and at room temperature, its capacity will naturally decline. During storage, the battery’s stored capacity gradually decreases, and the proportion of the reduced capacity relative to the rated capacity is called the self-discharge rate (nickel-cadmium and nickel-metal hydride batteries have a higher self-discharge rate compared to lithium-ion batteries). Typically, environmental temperature greatly affects this, with high temperatures accelerating self-discharge. The expression method and unit for battery capacity decay (self-discharge rate) are: %/month. Nickel-cadmium and nickel-metal hydride batteries have a self-discharge rate of 20–25%/month, while lithium-ion batteries have a self-discharge rate of 2–5%/month.
Cycle life:A single charge and discharge cycle of a secondary battery is called one cycle or one loop. Under certain discharge conditions, the number of cycles a battery undergoes before its capacity drops to a specified value is called the cycle life. With repeated charge and discharge usage, the capacity of a secondary battery gradually declines. Typically, based on the battery’s rated capacity, the number of charge and discharge cycles when the battery capacity drops to 60% or 80% of its rated capacity is referred to as the cycle life.
Memory effect:The memory effect of a battery refers to the percentage of charge that a not-fully-discharged battery can accept during the next charging session. To eliminate the memory effect, the battery must be fully discharged before recharging. Only by doing so can the battery be 100% fully charged. The memory effect causes inconvenience for fast charging of the battery. For nickel-cadmium batteries, charging them without full discharge may prevent the capacity from returning to its original standard, but performing a deep discharge followed by a high-current charge may restore the capacity. Neither nickel-metal hydride nor lithium-ion batteries have a memory effect.
Lithium-ion batteries have a relatively high single-cell discharge voltage platform of 3.6V, which is three times that of common batteries like nickel-metal hydride or nickel-cadmium. Therefore, they are very suitable for applications requiring a high discharge voltage platform. Because of the high discharge voltage, their size can also be significantly reduced. The discharge voltage range of lithium-ion batteries is generally 2.5–4.2V per cell.
Lithium-ion batteries also have rather special usage requirements. Their voltage must be controlled within 2.5–4.2V per cell. If the voltage is too low during use, it will reduce the battery’s lifespan, and if the charging voltage is too high, it may cause an explosion. Therefore, lithium-ion batteries cannot be used alone but must be equipped with electronic protection circuits to ensure they operate within the allowed range, thereby guaranteeing the safety of lithium-ion batteries and effectively extending their lifespan. Due to the special nature of lithium-ion batteries, their chargers also have quite high requirements. The ideal charging method for lithium-ion batteries is constant current and constant voltage: first charging at constant current to 4.2V per cell, then switching to constant voltage charging. Charging stops when the current drops to a certain level. Lithium-ion batteries also have relatively high requirements for charger voltage precision. A voltage lower than the rated value (4.2V) by 0.1V will result in undercharging, losing about 15% of the charge. A voltage higher than the rated value (4.2V) by 0.1V will cause overcharging, affecting the battery’s lifespan. Moreover, the charging current for lithium-ion batteries must not be too large and must match the battery’s capacity. Therefore, chargers for lithium-ion batteries must be specially developed for their characteristics and cannot be used interchangeably with chargers for other types of batteries.