Edward Benjamin, Senior Managing Director of eCycleElectric Consultants LLC.
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 on line – 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 it’s 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 electro chemical 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 over charged, over heated, 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 – Describes the energy storage capacity of a cell or battery.
Voltage – describes the energy potential of the current supplied by a cell or battery.
Battery Management System – a microchip controlled device that prevents (by limiting or shutting down the battery) over charge, over discharge, temperature events (thermal runaway), short circuits, and more. It also improves battery life and performance by balancing the cells, and provides information that can be used for determining battery health, state of charge, and more. These are necessary on advanced batteries such as NiMH, LiMa, LFP. There are some claims of lithium batteries that do not need such systems, but the most common industry practice is to use a BMS.
Cycle Life – how many times a battery can be charged and discharged before it has suffered significant degradation of performance. A deep cycle is discharging the battery all the way to the safe limit, and recharging it to full capacity. A shallow discharge is to discharge it only a little and then recharge to full. Nominal cycle life is based on deep cycles.
Max Current – How fast energy can be drawn from that battery – this limits torque, acceleration, etc.
C Rate – Another way of describing how fast energy can be drawn from a battery.
Recharge rate – how quickly energy can be returned to the battery as a function of charging.
Nominal voltage – the unique-to-the-metallurgy voltage that a cell should create.
Battery voltage – the current supplied by a collection of cells.
Parallel and Series connections – these determine the voltage of a battery package, as cells wired in parallel will deliver the nominal voltage, and cells wired in series (your common flashlight) will add each cells voltage. So battery designers will create batteries where some cells are Parallel (P) and some are in Series (S) resulting in descriptions like this. My flashlight is wired 2 S. Each cell has 1.5 volts, and the bulb is designed for 3.0 voltage operation. If I wired those two cells in parallel, I would have a very dim light because the bulb would only receive 1.5 volts.
Batteries are expensive. The large format batteries used on electric bikes and scooters can be very expensive. It is worthwhile to take care of them.
Most Popular: Lead Acid Batteries
Also refereed to as Pb, PBA, and as SVRLA, these are the most commonly used batteries for electric bikes worldwide. They are the same metallurgy as the batteries used to start your car, for your UPS for your computer. They are a very well understood technology that has been in commercial use for more than 110 years.
These look like the same batteries that are in your Uninterruptable Power Supply, or in the emergency lighting fixtures in big buildings. They are rectangular black plastic blocks with two terminals and a sticker that declares the size, capacity and voltage of this battery.
Lead acid battery strengths: Inexpensive, can be very well made (depending on the supplier), 100% recyclable, can support high rates of discharge, and rarely have any issues with fire or explosion (although it can happen!). They are available from a variety of makers, distributors and retailers in standard sizes and shapes. Cycle life can vary widely by maker – but the generally expected rate is 300 cycles, with many more resulting from “shallow discharge” or recharging after a short period of use. (There is no memory effect, and this shallow discharge / charge cycle is what you create when using them as starter batteries for your car – and realizing thousands of cycles.)
This metallurgy does not need a battery management system.
Lead acid battery weaknesses: Heavy, sometimes poorly made, less energy storage for the weight and volume than other metallurgies, relatively short lived, operates only in a narrow range of temperatures, (as with your car, when these are below freezing, they do not have much oomph. And when they are in high ambient temperatures, they do not last more than a few months.), Wide range of quality and performance, sometimes not correctly labeled. If short-circuited, the high rate of discharge can cause arcs, rapid heating of wires, and possible explosion. Lead is toxic, and the manufacture of such batteries has many hazards. These self discharge, about 20% per month, and need to be recharged at least every 3 months when not in use.
Nominal voltage for Lead Acid can be confusing. Almost all Lead Acid cells are manufactured as part of battery of 3 or 6 cells and measuring just one cell can be difficult. Additionally, Lead Acid voltage varies depending on the state of charge, varying from as low as 1.2 to 2.3 volts. Normal operation should be 1.75 volts or higher, with lower voltages resulting in damage to the cells.
But this same wide variation in voltage, dependent 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 SOC.
This metallurgy has never been popular for ebikes in the USA, but was widely used in Japan and to a lesser extent in Europe. Since Ni Cad cells contain cadmium, which is extremely toxic, many countries have banned such batteries. The superior performance of NiMH and Lithium metallurgies has also helped displace them.
If you have an older Japanese made bike or system, there is a remote chance that it has Ni Cad cells. Measure the nominal voltage. Ni Cad nominal voltage is 1.2 volts. The cells are cylindrical, and look like normal “flashlight” batteries.
These cells were used in many rechargeable battery applications in the past. Today they are still used in some special applications, but not in electric bikes.
If you have Ni Cad ebike battery…it is old, my suggestion is to look into replacing it with a NiMH battery or a Lithium battery. Ni Cads suffer from memory effect, and they are lower in energy storage than NiMH or Lithium, but usually more expensive now. BTW, Ni Cad is toxic and should not be casually discarded – take it to a recycler.
NiMH or Nickel Metal Hydride
This metallurgy has better performance than Ni Cad or Lead Acid, but not as good as Lithium. So it enjoyed a short reign as the advanced battery of choice (do you remember when your cell phone shrank from the size of a hardback book to something that fit in your pants pocket? That was the advent of NiMH. When the phone shrank to shirt pocket size – that was the advent of lithium. )
Nominal voltage is 1.2 volts, and cells are cylinders that look like flashlight batteries.
Only a few electric bikes that made it to the USA use or have used these cells. They are quite common in Japan and Europe. Some notable brands that use or used NiMH are Sparta, Tidal Force, Yamaha, Panasonic and Sanyo.
NiMH battery strengths: Much lighter and more compact than lead acid, with excellent high discharge rates, excellent recharge rates, durable, and with cycle life in the range of 500+. Not toxic. Can be recycled.
NiMH battery weaknesses: Lithium is often less expensive, and works even better. Batteries that have warmed up during use must cool before they will accept a charge. They do not work well in temperatures below freezing. Charging at wrong voltage can damage and cause risk of fire. These self discharge at a rate of about 30% per month.
These batteries require a BMS.
Lithium batteries are actually several different types. A quick look at Wikipedia shows a chart that is bewildering in the variety of “lithium” metallurgies.
An important thing to know about lithium batteries is this: Using the wrong charger, the wrong lithium battery, or a poorly made lithium battery, or a defective lithium battery can result in a wicked fire that can start as an explosion.
Have I scared you? Don’t be too scared, for your phone, computer, tablet, MP3 player, and more all use lithium batteries. If you are reading this, you have survived tens of thousands of recharge cycles of lithium batteries – and if you look at the owner’s manual for all those devices, they all warn you of fire and explosion if not charged properly.
And since nearly all lithium ebike batteries are equipped with a Battery Management System, the normal result of any irregularity in the battery function is for the BMS to shut the battery down completely. This is rare, and the consequence is a walk home or a call to get a ride. Note: BMS can fail, or be damaged. It is prudent to be alert to such possibilities.
There are two lithium metallurgies that are popular for electric bikes today:
Lithium Manganese sometimes referred to by a more complete name that will mention cobalt. I will refer to these as LiMa. Nominal voltage is 3.7 volts.
Lithium Iron Phosphate, also called LFP. Nominal voltage is 3.3 volts.
Both of these metallurgies can come in the familiar cylindrical cells, or in aluminum foil / polymer cells in rectangular shapes. Sometimes called soft packs, and having a space age look to them. Some are in rectangular steel or aluminum cans.
When comparing LiMa and LFP, the primary noticeable difference is that LFP is bulkier for the same energy storage than LiMa.
This means that for most electric bike applications, LiMa is a better choice (more compact) than the LFP. But for motor scooter, or some other applications, LFP may be preferred. But…there are electric bikes using both types of lithium on the market and in wide use.
There are claims that LFP is “safer” than Li Ma. The claim is that LFP is inherently less flammable than LiMa. This is true, but the practical reality for most ebike users is that a well designed, well made, and undamaged LiMa battery works very well, and is safe. And LFP actually can burn – Google it. Incidents with either metallurgy are rare. When they do occur, it is often the result of the cells being made by a low cost provider of dubious capability and sold at a low price.
Lithium battery strengths: More compact, lighter in weight, wide range of temperature, low self discharge in the area of 5% per month, non toxic, recyclable, stores a lot of energy, cycle life can be up to 1000 cycles or maybe more.
Lithium battery weaknesses: More expensive, (though quite affordable now) flammable, wide variations in quality of cell and battery depending on the maker and battery assembler. Needs a sophisticated BMS, with a few makers claiming otherwise for their particular cells.
Practical Tips for Battery Care:
This applies to all batteries:
- Read the owners manual supplied with your bike. If any doubt, call the company and ask. Read the warning stickers. Be confident but cautious.
- Only use the charger that was supplied with your bike to charge your battery.
- Repeat! Only use the charger that was supplied with your bike to charge your battery.
- Check that the charger you received with your bike was the correct charger!
- Store bike, batteries, and charger in a dry place, out of the weather. Only operate the charger in a dry place.
- When charging the battery, place the battery, bike and charger in a place where any accident, such as a hot battery, hot charger, or even a (very, very rare) fire would not affect dwellings, damage property, or hurt people.
- Know where the fire extinguisher is, and be alert that not all fire extinguishers will work on battery fires. For those who are interested, there are training films on line for airline crew on how to extinguish a lithium fire in a laptop computer.
- Be alert to how long you have connected the charger. A smart charger is supposed to sense the battery state of charge and turn off when the charge is complete. This avoids the chance of over charging – a major cause of damage to batteries. As a backup, unplug the charger when not being used. Leaving the charger plugged in indefinitely is placing too much faith in the design and construction of the charger.
- If your charger is not a smart charger – be very alert to the time that you have charged the battery and unplug it when the charge is complete.
- Do not touch any part of the electrical system of an ebike, the battery, or the charger with your tongue. If you do, you will be regretting it for a long time and be too embarrassed to tell anyone what is wrong.
- You cannot go wrong by charging the battery after each use, although it may not be required.
- You cannot go wrong by charging the battery every month or perhaps every 2-3 months when not in use, even if not required.
- Be alert to the state of charge. There are some bikes that when they are “off” they are still using a bit of current, and that will discharge the battery to a level that can damage the battery. Removing the battery, or more frequent charging may be needed.
- Read the label on the charger. If you plug a 220V charger into a 110 volt mains outlet, you will not be pleased with the results. Even less so if it was a 110v charger that you plugged into a 220v mains. Unlike computers and cell phones – where nearly all chargers are dual voltage, many ebikes are shipped with a charger that can accept only one voltage. Since ebike makers sell bikes all over the world, it is possible for you to receive a charger for the wrong mains voltage, or even with the wrong plug.
- If you are trying to connect a charger to the bike or battery, and the plug does not fit – you may be making a mistake. Stop and evaluate. Ask questions of the maker and dealer.
- BMS (and smart chargers) are supposed to protect the bike and battery against damage and provide a level of safety from fire, electrical shock, and overheat. They almost always work. But…not always. Be alert and consider what will happen and what you will do, if the hardware has been damaged or failed and either the battery fails to charge, (most likely) or a fire occurs.
- Shock, vibration, high heat, sub freezing temperatures, water, high humidity, crushing, punctures, are all bad for batteries. Do what you can to prevent the exposure of your battery to such.
Thank you to Edward Benjamin, (Senior Managing Director of eCycleElectric Consultants LLC) for this thorough e-bike battery post.