Jan. 08, 2025
The battery is a crucial component of any e-bike and often the most expensive. It determines how long the bike can run on a single charge, its overall lifespan, weight, and other key factors. When selecting an electric bike, the battery should be given the highest consideration.
A well-chosen battery directly impacts efficiency and the distance covered per charge. Even with similar size and weight, batteries can perform differently depending on their type and structure. Key characteristics to consider include capacity, voltage, size, weight, charging time, and overall lifespan.
Most e-bike kits are designed to operate within a specific voltage range. For example, a typical 36V e-bike requires a battery that provides power between 30V and 42V. At 42V, the battery is fully charged and holds its maximum energy; at 30V, it should automatically shut down to prevent permanent damage. This function is managed by the Battery Monitoring System (BMS). The commonly referenced "36V" is the average operating voltage, also known as the nominal voltage. Voltage, measured in volts (V), describes the speed at which electrons move—higher voltage means greater speed!
Capacity refers to the amount of energy a battery can store and is its primary characteristic. It is measured in ampere-hours (Ah), representing the fixed number of amps a battery can provide in one hour (C rate). For example, doubling the amps will halve the usage time to 30 minutes, while halving the amps will extend it to two hours.
Each battery has a limited number of charge-discharge cycles, after which its capacity begins to decrease proportionally. For instance, if a battery is discharged by 10% and then recharged, it counts as one cycle.
The actual lifespan of a battery is determined by the total number of cycles it can undergo, which largely depends on its operating conditions. Deeper discharges generally result in fewer overall cycles.
Lead (gel) batteries are the oldest type of e-bike battery and are increasingly falling out of use. The primary reason is their low capacity. These batteries are notably heavy, making the bike significantly bulkier. Additionally, they have a slow charging time, requiring 8-10 hours for a full charge. Their lifespan is also limited, lasting only 150-200 cycles.
The most popular and optimal type of battery for an e-bike today. A lithium battery has the best combination of total weight and capacity. The specific capacity of lithium-ion batteries is the highest of all existing types and this is their main advantage. Lithium-ion batteries do not have the 'memory' effect.
Lithium-ion batteries have some disadvantages, including sensitivity to temperature variations and limited fast-charging capability. They are prone to overheating and require careful discharge management. Over time, they experience aging and capacity loss. However, their lifespan is significantly longer than lead-acid batteries, offering around 400 cycles—approximately 2.5 times more.
E-Bike Lithium Battery packs must be specifically designed to include a Battery Management System (BMS). This essential circuitry regulates current draw to meet motor requirements, prevents excessive discharge, and ensures balanced charging among individual cells. The BMS plays a crucial role in maintaining battery performance and longevity.
Li-Po batteries are primarily favored by cell phone manufacturers but are not suitable for operating e-bikes due to their inability to handle impacts and vibrations during rides. They are designed for environments like electric cars, where vibrations are minimal, and are also common in aircraft models where weight is a critical factor. However, these batteries pose a significant fire risk. Under unfavorable conditions such as short circuits, BMS failure, or accidents, there is a high likelihood of ignition.
LiFePo4 batteries are a newer and increasingly popular choice. Their advantages include excellent frost resistance, functioning at temperatures as low as -30°C without capacity loss, and fast-charging capability. They boast the highest cycle life, with approximately 1,000 full cycles, and are less prone to aging than standard Li-ion batteries. Additionally, they do not suffer from the memory effect. The primary disadvantages are their lower specific capacity and higher cost compared to other battery types.
How can I avoid destroying the battery?
Pay attention to the battery's on/off system. Renowned manufacturers incorporate a 'sleep mode' in their batteries. You typically activate the battery by pressing a button or turning on the e-bike via the control display. Once the e-bike is turned off, the battery will automatically enter sleep mode after a few hours, shutting off power from the BMS system. To continue riding, you need to press the button again to reactivate the battery.
How do I store the battery in winter?
Storing the battery during winter is simple. Charge it to 50% and store it in a cool place. It’s best to store the battery outside the e-bike to prevent accidental activation.
The batteries heat up during charging, is something wrong?
No, it's normal. All battery types heat up during charging, as do their chargers.
What is the 'memory effect'?
The memory effect occurs when a battery is recharged before being fully discharged. The battery 'remembers' the remaining capacity before the next charge, reducing its usage time. However, most modern batteries like Li-ion and Li-Po have little to no memory effect.
What does self-discharge mean?
Self-discharge refers to the gradual loss of energy when a fully charged battery is not in use. For Li-ion and Li-Po batteries, this value is minimal, about 5% per month at room temperature. It’s recommended to check the battery monthly and, if its capacity falls below 50%, recharge it to approximately 70%.
Deep discharge makes the battery harder to use and reduces its future capacity. Oxidation in lithium batteries negatively impacts both capacity and lifespan. If the battery is switched off for an extended period (e.g., during winter), fully charge it at least once every 90 days.
Do not charge the battery immediately after riding. Let it cool down first, as charging a heated battery prevents proper cooling and accelerates degradation.
Charging beyond 80% (around 40V) increases the battery's internal resistance, causing it to heat up more and degrade faster. Only fully charge the battery when absolutely necessary.
High temperatures and frost affect battery performance and lifespan. Avoid storing the battery in temperatures below 0ºC or above 30ºC. Also, avoid prolonged exposure to direct sunlight, such as leaving it parked under the sun.
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