Electric bikes are equipped with a wide variety of batteries, and this guide will provide basics on the prevention of damage, and care for such diverse systems.
But it is important that the reader refer to the specific instructions given in the owner’s manual for their bike, their battery, and their charger. If you do not have that document, check online – many such manuals are posted at the website of the brand. Or contact the folks who sold the bike and ask them for a copy. Read all warning labels and tags – and then follow their instructions.
A “battery” is a collection of cells that work together to achieve a desired voltage and watt hours (capacity) for the bike. Although it is correct to refer to the individual energy storage devices as cells, common usage is to refer to both cells and the complete battery as “batteries”.
There are a number of different types of cells used in electric bikes. If you want to sound like a battery expert, refer to them as “different metallurgies”. Each metallurgy has its strengths, weaknesses, and different requirements for care and safety. If you do not know what metallurgy your bike battery uses, ask the maker, for this can be a very important fact. Treating the battery in the wrong way can result in fire, explosion, or more commonly – a ruined battery.
Cells use an electrochemical reaction to produce electrical current. The voltage of that current is specific to the composition of the cell, and the capacity (amount of energy – also called watt hours or amp hours) is a function of the design and volume of the cell. We can determine the metallurgy of a cell by measuring the voltage that a fully charged cell puts out. (Just one cell! The voltage of the battery will be a function of the number of cells, the voltage of those cells, and how they are connected.)
Cells are active for only a few years at best, often less time than that. They can be damaged when their state of charge falls below a certain value, or when they are overcharged, overheated, crushed, penetrated, etc. Such damage reduces cell performance – sometimes to zero.
Some terms that you will need as you read on:
Amp Hours – Describes the energy storage capacity of a cell or battery.
Watt Hours – Energy Storage Capacity
Watt Hours refers to the amount of energy that a cell or battery can store. It quantifies the capacity of the battery to hold and release power.
Voltage – Energy Potential
Voltage defines the energy potential of the current produced by a cell or battery. It represents the force with which the energy is supplied.
Battery Management System – Enhanced Battery Control
A Battery Management System, also known as a BMS, is a sophisticated device controlled by a microchip. Its primary function is to prevent overcharging, overdischarging, temperature-induced malfunctions, short circuits, and other potential battery hazards. Additionally, it optimizes battery life and overall performance by ensuring cell balance and providing crucial information for battery diagnostics and monitoring.
Cycle Life – Battery’s Charging and Discharging Capacity
Cycle Life refers to the number of times a battery can be charged and discharged before it experiences significant decline in performance. A deep cycle entails fully discharging the battery to its safe limit and then charging it to its maximum capacity. On the other hand, a shallow discharge involves partially discharging the battery and subsequently recharging it completely. Nominal cycle life is typically based on deep cycle usage patterns.
Max Current – Limiting Energy Release Rate
Max Current denotes the maximum rate at which energy can be drawn from a battery. This parameter restricts the torque, acceleration, and other energy-dependent parameters in the system.
C Rate – Energy Withdrawal Speed
C Rate provides an alternative method of describing the rate at which energy can be withdrawn from a battery. It specifies how fast the energy can be discharged.
Recharge Rate – Speed of Energy Refill
Recharge rate signifies the speed at which energy can be replenished in the battery during the charging process.
Nominal Voltage – Unique Metallurgical Voltage
Nominal voltage corresponds to the specific voltage level that a single cell should generate based on its metallurgy composition.
Battery Voltage – Combined Cell Output
Battery voltage represents the cumulative electrical output produced by a collection of cells that are interconnected.
Parallel and Series Connections – Determining Battery Voltage
Parallel and series connections play a significant role in determining the overall voltage of a battery pack. When cells are wired in parallel, the resultant voltage is equal to the nominal voltage of those cells. Conversely, cells wired in series contribute to the summed voltage across all the individual cells. It is common for battery designers to combine cells in parallel (P) and series (S), resulting in varied voltage descriptions. For instance, a flashlight might be wired with 2 cells in series, each having a voltage of 1.5 volts. This configuration provides a total voltage of 3.0 volts, ensuring optimal bulb operation. It is important to note that if these two cells were connected in parallel, the resulting voltage would only be 1.5 volts, which would result in dim illumination for the bulb.
Batteries are a valuable investment, especially when it comes to large format batteries used in electric bikes and scooters. It is essential to prioritize their maintenance and care to ensure long-lasting performance and minimize financial burden.
Most Popular: Lead Acid Batteries
Lead Acid Batteries, commonly referred to as Pb, PBA, and SVRLA, are the most widely used batteries in the electric bike industry worldwide. They share the same metallurgical composition as the batteries used for starting cars and providing uninterrupted power supply for computers. Lead Acid Batteries are a well-established technology with over 110 years of commercial utilization.
These batteries closely resemble the ones found in Uninterruptable Power Supplies or emergency lighting fixtures in large buildings. They are rectangular black plastic blocks with two terminals and a label specifying their size, capacity, and voltage.
Strengths of Lead Acid Batteries:
Lead Acid Batteries offer several advantages, including affordability, high-quality construction (depending on the supplier), 100% recyclability, ability to support high discharge rates, and a low risk of fire or explosion (although rare instances can occur). They are readily available from various manufacturers, distributors, and retailers in standard sizes and shapes. The cycle life of Lead Acid Batteries can vary significantly depending on the manufacturer, but it is generally expected to be around 300 cycles. However, when utilizing shallow discharge and charge cycles, such as in starter batteries for cars, batteries can even experience thousands of cycles due to the absence of memory effect.
This metallurgy does not require a battery management system
Weaknesses of lead acid batteries: Lead acid batteries are heavy and sometimes poorly made. They provide less energy storage for their weight and volume compared to other metallurgies. They also have a relatively short lifespan and can only operate within a narrow temperature range. For instance, in freezing temperatures, lead acid batteries lose their power, while in high ambient temperatures, they do not last more than a few months. Furthermore, lead acid batteries vary in quality and performance, and are sometimes inaccurately labeled. In the event of a short-circuit, the high rate of discharge can cause arcs, rapid heating of wires, and even explosions. It is important to note that lead is toxic, and the manufacturing process of these batteries poses several hazards. Additionally, lead acid batteries self-discharge at a rate of about 20% per month and need to be recharged at least every 3 months when not in use.
Nominal voltage for Lead Acid:
Understanding the nominal voltage for lead acid batteries can be challenging. Most lead acid cells are manufactured as part of a battery containing 3 or 6 cells, making it difficult to measure the voltage of a single cell. Moreover, the voltage of lead acid batteries varies depending on their state of charge, ranging from as low as 1.2 to 2.3 volts. Ideally, the normal operating voltage should be 1.75 volts or higher, as lower voltages can damage the cells.
However, this wide variation in voltage, which depends on the state of charge, makes it relatively easy to measure the amount of energy in the battery and display it as a fuel gauge or state of charge (SOC) indicator.
This metallurgy has never gained popularity for ebikes in the USA, but it was widely used in Japan and to a lesser extent in Europe. Ni Cad cells contain cadmium, which is extremely toxic, leading to the banning of such batteries in many countries. Additionally, the superior performance of NiMH and Lithium metallurgies has played a role in displacing Ni Cad batteries.
If you have an older Japanese-made bike or system, there is a small possibility that it uses Ni Cad cells. To determine this, measure the nominal voltage, which should be 1.2 volts for Ni Cad. These cells are cylindrical in shape and resemble normal “flashlight” batteries.
Although Ni Cad batteries were once used in various rechargeable battery applications, they are no longer commonly employed in electric bikes. If you have a Ni Cad ebike battery that is old, it is advisable to consider replacing it with a NiMH battery or a Lithium battery. Not only do Ni Cads suffer from memory effect and have lower energy storage compared to NiMH or Lithium batteries, but they are also usually more expensive nowadays. Furthermore, it is important to remember that Ni Cad batteries are toxic and should not be casually discarded. Instead, they should be taken to a recycler for proper disposal.
NiMH or Nickel Metal Hydride
This metallurgy offers better performance than Ni Cad or Lead Acid, although it is not as good as Lithium. Therefore, it experienced a brief period as the preferred advanced battery choice (do you recall when cell phones transitioned from the size of a hardback book to something that could fit in your pants pocket? That was the era of NiMH. As phones continued to shrink to shirt pocket size, lithium batteries emerged.)
The nominal voltage for NiMH batteries is 1.2 volts, and they have cylindrical shapes resembling flashlight batteries.
Only a few electric bikes that made it to the USA utilize or have utilized NiMH cells. However, they are quite common in Japan and Europe. Some notable brands that use or have used NiMH batteries include Sparta, Tidal Force, Yamaha, Panasonic, and Sanyo.
Strengths of NiMH batteries:
NiMH batteries are significantly lighter and more compact than lead acid batteries. They offer excellent high discharge rates, recharge rates, durability, and have a cycle life in the range of 500. Furthermore, NiMH batteries are not toxic and can be recycled.
**Weaknesses of NiMH batteries:**
NiMH batteries are not as cost-effective as lithium batteries, which perform even better. They require time to cool down before accepting a charge after being used. Additionally, they do not function optimally in freezing temperatures. It is important to avoid charging them at the wrong voltage as this can cause damage and potentially lead to a fire hazard. NiMH batteries also self-discharge at a rate of approximately 30% per month.
**Overview of Lithium batteries:**
Lithium batteries encompass various types and compositions. A glance at a comprehensive chart on Wikipedia reveals the bewildering assortment of different “lithium” metallurgies available.
There is a crucial aspect to consider when dealing with lithium batteries: the use of an incorrect charger, a mismatched lithium battery, a poorly manufactured battery, or a defective battery can result in a dangerous fire that may even manifest as an explosion.
Despite the potential risks, there is no need to be excessively alarmed, as lithium batteries are commonly used in devices such as phones, computers, tablets, and MP3 players. If you are reading this, it means that you have successfully handled numerous recharge cycles of lithium batteries. However, it is essential to acknowledge the warning messages regarding fire and explosion risks if these batteries are not charged properly, which are often highlighted in the respective owner’s manuals.
Furthermore, most lithium ebike batteries are equipped with a Battery Management System (BMS), which typically shuts down the battery in the event of any irregularity in its function. While such occurrences are rare, it is always wise to remain vigilant as BMS can fail or become damaged. In such cases, one may need to walk home or seek assistance.
Currently, two lithium metallurgies dominate the electric bike industry:
1. Lithium Manganese, sometimes referred to as LiMa, with a nominal voltage of 3.7 volts. These batteries are available in both cylindrical and rectangular shapes, the latter often featuring aluminum foil/polymer cells that boast a futuristic appearance. Some variations even come in rectangular steel or aluminum cans.
2. Lithium Iron Phosphate (LFP), also known as LiFePO4, with a nominal voltage of 3.3 volts.
When comparing LiMa and LFP, the most noticeable distinction lies in their size for the same energy storage capacity. LFP batteries are bulkier compared to LiMa batteries. As a result, for most electric bike applications, LiMa batteries are the preferred choice due to their compact nature. However, in specific cases such as motor scooters, LFP batteries may be more suitable. Nevertheless, it is worth mentioning that electric bikes incorporating either type of lithium battery are commonly found on the market and widely used.
There are assertions regarding the “safety” of LFP batteries compared to LiMa batteries. It is true that LFP batteries are inherently less prone to flammability than LiMa batteries. However, in practical terms, a well-designed, well-manufactured, and undamaged LiMa battery functions excellently and is safe. In fact, LFP batteries can also burn under certain circumstances, so it is crucial to conduct thorough research. Incidents involving either lithium metallurgy are infrequent and often stem from low-cost providers offering subpar quality batteries at reduced prices.
**Advantages of Lithium batteries:**
Lithium batteries possess a multitude of strengths, making them highly desirable. These advantages include their compact size, lightweight nature, capability to operate under a wide range of temperatures, low self-discharge rate (approximately 5% per month), non-toxic composition, recyclability, ability to store a substantial amount of energy, and a cycle life of up to 1000 cycles or potentially more.
**Weaknesses of Lithium Batteries:**
Lithium batteries, although now quite affordable, still have certain drawbacks. One of the main concerns is their flammability. Additionally, the quality of the battery and cell can vary significantly depending on the manufacturer and assembler. A sophisticated Battery Management System (BMS) is crucial for optimal performance, despite some makers claiming otherwise for their specific cells.
Useful Tips for Battery Maintenance:
These tips apply to all types of batteries:
- Take the time to read the owner’s manual provided with your bike. If you have any doubts, don’t hesitate to contact the company for clarification. Pay close attention to any warning stickers. Confidence is important, but caution is key.
- Always use the charger that came with your bike to charge the battery.
- Repeat! Only use the charger provided with your bike to charge the battery.
- Double-check that the charger you received is the correct one for your bike.
- Ensure that your bike, batteries, and charger are stored in a dry place, away from any harsh weather conditions. Only use the charger in a dry environment.
- When charging the battery, place it, along with the bike and charger, in a safe location where any potential accidents, such as a hot battery or charger, or an extremely rare fire incident, wouldn’t harm people or property.
- Know the location of the fire extinguisher and keep in mind that not all fire extinguishers are suitable for extinguishing battery fires. If you’re interested, there are online training films available for airline crew on how to extinguish a lithium fire in a laptop computer (Watch here).
- Be mindful of how long you keep the charger connected. A smart charger should automatically turn off when the battery is fully charged to prevent overcharging, which can lead to battery damage. As a precautionary measure, unplug the charger when not in use. Relying solely on the charger’s design and construction is risky.
- If you have a non-smart charger, pay close attention to the charging time and unplug it once the battery is fully charged.
- Avoid touching any part of the electrical system of an e-bike, the battery, or the charger with your tongue. Such an action would lead to long-lasting regrets and an embarrassing tale to share.
- Charging the battery after each use is a reliable practice, even if it may not be necessary.
- When the battery is not in use, consider charging it every month or every 2-3 months to maintain its health, even if it’s not mandatory.
- Stay vigilant regarding the battery’s state of charge. Some bikes may use a small amount of current even when they are turned off, which can drain the battery and cause damage. It may be necessary to remove the battery or increase the frequency of charging.
- Refer to the label on the charger. Plugging a 220V charger into a 110V outlet, or vice versa, will undoubtedly yield undesirable results. Unlike computers and cell phones, which usually have dual-voltage chargers, many e-bikes come with chargers that can only accommodate one voltage. It’s possible to receive a charger with the wrong mains voltage or plug, considering that e-bike manufacturers sell their products worldwide.
- If you encounter difficulties when connecting a charger to your bike or battery, and the plug doesn’t fit, pause and reassess the situation. Seek guidance from the manufacturer or dealer before proceeding.
- Battery Management Systems (BMS) and smart chargers are designed to safeguard the bike and battery from damage, as well as provide protection against fire, electric shock, and overheating. They usually work flawlessly, but there may be occasional failures. Stay vigilant and contemplate the potential consequences and necessary actions if the hardware is compromised, leading to either a failed battery charging (a more likely scenario) or a fire incident.
- Shock, vibration, high heat, sub-freezing temperatures, water exposure, high humidity, and crushing can all have detrimental effects on batteries. Take preventive measures to shield your battery from such hazards.
A special thank you to Edward Benjamin, the Senior Managing Director of eCycleElectric Consultants LLC, for sharing this comprehensive guide on e-bike batteries.