Skip to main content

Battery is the costliest component in an electric bike and for good reason. It’s the lifeblood of your bike and without it fueling your motor, good luck climbing that hill. Even though eBikes have been around for quite some time now, there are still many questions that surround eBike batteries. Luckily for you, I’ll discuss everything there’s to know about electric bike batteries in this detailed blog. 

Here’s what I’ll be covering.

So, let’s start!

Which Batteries Do eBikes Use?

Just like most electrical devices today, electric bikes use Lithium-ion batteries (Li-ion cells packed in a casing). 

Lithium-ion batteries are rechargeable and can handle hundreds of charges and discharges, with high-end options rated at up to 1,000 cycles. These batteries are much lighter compared to all other options because their electrodes are made of lithium and carbon – both of which are among the lightest elements in the world.

Compared to that, lead-acid batteries use lead electrodes and are, therefore, quite bulkier. Likewise, nickel-cadmium (NiCd) and nickel-metal hydride (NiMH) batteries are also much heavier than Li-ion batteries. 

Besides being lightweight, Lithium-ion batteries pack much more energy than all other commercial alternatives… because Lithium is a highly reactive metal and can store a great amount of energy in its atomic bonds.

For instance, a Li-ion that packs 300 watt-hours of electrical energy weighs around 4.4lbs (2kg). A NiMH or NiCd battery of similar energy content would weigh around 9lbs (4kg), while a lead-acid battery would weigh a whopping 26.5lbs (12kg). Since you don’t want that much weight slowing you down, Lithium-ion batteries have become an industry standard for eBikes despite their significantly more cost. 

Li-ion batteries also don’t have toxic heavy metals in them, unlike lead-acid, nickel-metal hydride, nickel-cadmium, and other commercial batteries. They also have no memory effect, which means you don’t need to discharge them completely before recharging. Moreover, they also hold their charge for a much longer time than other batteries.

And as I said earlier, they can last hundreds to a thousand charge cycles in most cases. But I don’t mean Lithium-ion batteries are flawless… they do have their fair share of downsides too. 

For instance, they’re quite sensitive to extreme temperatures and degrade much faster when exposed to high temperatures for a prolonged duration. They lose their efficiency when you repeatedly drain them completely. 

Moreover, they need an on-board computer for battery management… and can very rarely burst into fire when the battery pack fails. But despite these downsides, Li-ion batteries are much better than every other commercial alternative.

How Electric Bike Batteries Work?

Well, I’m not going to explain how electrons move from anode to cathode as this is not Physics 101. I’ll be describing how an eBike battery works with other components of the bike.

A visual representation of battery pack & battery cells in the Miclon Cybertrack 100. (Image Credit: Miclon)

Electric bike batteries can be thought of as the fuel tank of a car. Just as pushing the accelerator injects fuel from the tank into the engine, pedaling the cranks does the same thing in electric bikes.

When you pedal your bike, your pedal input is sensed either by a cadence sensor (that detects how fast you’re pedaling) or a torque sensor (that detects how hard you’re pedaling). If you want to explore more about how these two types of sensors differ from each other, check out this in-depth torque vs cadence comparison.

Anyways, the sensor relays the message to the eBike controller, which uses that message to decide how much current to ‘pull’ from the battery and ‘push’ to the motor. Having a controller that can regulate more amps (A) of current means you will have better acceleration as well as better hill climbing ability. 

To understand how much charge a battery can store inside it and how the battery capacity interacts with the powertrain to dictate how long you would be going on a single charge, you need to understand all the parameters you see on a battery pack.

What are Volts, Amps, Watts?

Volt is a measure of voltage – which, in simple terms, can be thought of as the “pressure” that causes electricity to flow in a circuit. Without voltage, current can’t flow in a circuit. 

If a battery has higher voltage or volts (V), it can ‘push’ more electricity out of it at any given instant than the one with lower voltage. In other words, having higher volts translates to more power, rapid acceleration, and more speed. 

Like other electronic devices, eBike batteries are also designed to work at a specific voltage. A 48V battery will have twice as much ‘electricity pushing power’ as a 24V battery so it will be much more capable.

Amp or Ampere measures the amount of electric current, that’s how many electrons are flowing through a circuit. More amps means more electrons or more current. Watts is the combination of both Volts and Amps (Watts = Volts x Amps) and is used to show power. 

An easy way to understand the difference between volts, amps, and watts is to use the analogy of water coming out of a hose.

Voltage is the pressure that’s causing the water to flow, as water won’t flow without a pump or something else pressuring it to flow. Increasing the pressure (or voltage) will lead to more water flowing out of the hose.

Amp is the quantity of water flowing through the hose, which can be increased by increasing the diameter of the hose. The more the amps, the bigger the hose will be, and the more water will flow out of it.

Watt is a bit difficult to understand with this analogy but you may consider it as the total amount of water that has flowed out of the hose. Now this total amount (Watts) can be increased by increasing either the pressure (Voltage) or the diameter of the hose (Amps) so that more water can flow through it. 

Amp Hours (Ah) vs Watt Hours (Wh)

Both amp hours (Ah) and watt hours (Wh) can give you an idea about the capacity of your battery, though the latter also factors in your voltage. 

Amp hours measure how many Amps (or how much current) a battery can deliver for an hour. 

Shimano is one the leading manufacturer of electric bike (ebike) batteries

Battery volts, amps, amp hours, and watt hours shown on Shimano BT-E8035 eBike battery. (Image Credit: Shimano)

For instance, a 20Ah battery can deliver 1 amp of current for 20 hours (1A x 20h = 20Ah), or 20 amps for an hour (20A x 1h = 20Ah) , or 10 amps for 2 hours (10A x 2h = 20Ah) or 40 amps for half an hour (40A x 0.5h = 20Ah)… you get the point.

In other words, a 20Ah battery will run for twice as long as a 10Ah battery, provided that the voltage and other restraints are same… and it’s due to these other restraints, amp hour (Ah) alone can’t give you an accurate idea of what to expect from a battery.

Watt hours, on the other hand, is a much better way to find out the ‘actual’ capacity of a battery in your eBike because it does that in relation with your overall powertrain. Besides just reflecting the amp hours or the charge holding capacity of your battery, it also factors in the voltage of your power system to determine how far you will be able to go on a full charge. 

It means, watt hours can give you an accurate picture of how much ‘energy’ your battery packs… and that’s why this number is what you should look for to determine the potential range of an eBike battery.

For instance, a 500Wh battery can deliver 500 watts of power (say operating a 500W motor on throttle/ pure electric mode) for an hour. In case it operates a 250W motor (or delivers 250 watts of continuous power) in pure electric mode, it will be able to do that for 2 hours. Likewise, if it operates a 1000W motor (or delivers 1000 watts of continuous power) on throttle, it will be drained within 30 minutes. 

Since you usually don’t use a continuous level of power at all times, it’s hard to accurately calculate how much ride time you’ll get based on the Wh capacity of your battery, but the main thing to understand is that, the more watt hours (Wh) you have, the more mileage you will get from your battery.

Converting Amp Hours Into Watt Hours

The relationship between amp hours and watt hours is fairly easy to understand. As I mentioned before, watt hours (Wh) factor in both the battery capacity (Ah) and the voltage (V), it can be calculated by this simple formula:

Watt hours (Wh) = Amp hours (Ah) x Voltage (V)

For instance, a 36V 10Ah battery would have an energy content of 360Wh, while a 48V 10Ah battery would have 480Wh of energy. It’s interesting to note that the battery capacity is the same in both cases (10Ah) but the energy content is different. 

It means that the eBike with the 48V 10Ah battery will not only have better acceleration and more top speed (due to more voltage), it will also have more mileage than the 36V 10Ah battery (despite the same Ah or charge holding capacity) due to more energy content or Wh. 

But you’ll only experience the increase in mileage if you use both eBikes at the same speed, as the faster you go, the more energy you consume. 

Understanding Battery Packs & Cells

The battery you see on your electric bike is actually a pack or casing that contains several Lithium-ion cells inside. The casing, usually made of plastic, is there to keep the battery cells in place and to protect them from vibration and impacts, whenever you tip over and fall down. 

Most manufacturers don’t reveal the type, number, and configuration of the cells they use in their battery packs, but most commonly you find 40-80 Lithium 18650 cells. In case you don’t know, 18650 refers to a cylindrical cell that has a diameter of 18mm and a length of 65mm. 

Thankfully, things have advanced to surprisingly new levels these days and a typical 18650 cell can hold up to 3500mAh. A decade ago, a typical 18650 cell could only hold upto 1000mAh… which means modern battery packs can deliver significantly more range for similar size packs!

This is how Li-ion cells are packed inside an eBike battery casing. (Image Credit: Vélo Electrique)

To understand how the individual output of these cells add up to the cumulative numbers you see on the battery pack, let’s see how many 18650 cells you need to make up a 48V 15Ah Lithium battery, assuming the cells are 3.7V 2500mA.

To get 48 volts, you need 13 batteries (13 x 3.7V = 48.1V) connected in series, as voltage adds up in series. If you do that, you’ll get what we call a 13S1P configuration. 

Though you’re getting 48 volts (the cumulative output of 13 3.7V cells), the current output will be the same as the output of each cell, that’s 2500mA or 2.5A. It’s because the current doesn’t add up in series… it adds up in parallel.

Now, to get more current, you’ll need to place several rows of the above 13S1P series in parallel. To get to 15Ah, you would need 6 cells in parallel (15Ah / 2.5A = 6) … or in other words, you would have to repeat the above configuration of 13-cell series six times.

So, you’d have a final configuration of 13S6P with 78 cells (13 x 6 = 78)!

As for the size and weight of the battery pack, the less these two parameters are (while ensuring the capacity and range you need), the better it will be. The battery pack can be both removable and non-removable in nature. 

The removable battery pack allows you to charge the battery inside your place, besides also reducing the risk of battery theft (though most manufacturers solve this problem by providing a lock and key with the battery). 

If you have a non-removable battery, you’ll have to charge your bike in the garage or wherever you store your bike. An internal battery also increases the overall aesthetics and people can hardly tell if you have a regular bike or an electric bike.

As for mounting the pack on your bike, you see a variety of arrangements. 

Having the battery mounted between the wheels, midway in your frame and preferably at a lower position, is a great arrangement as it evenly distributes your battery weight across the bike. 

Compared to that, having an asymmetric configuration – such as placing the battery pack on the rear rack – skews the weight distribution and impacts the ride handling at curves and hills. It also doesn’t look good.

Some manufacturers place the battery inside the top or downtube in a perfectly discreet manner, but still make them removable for out-of-frame charging, and that’s what I like the most.

Bosch is one the leading manufacturer of electric bike (ebike) batteries

A frame-integrated but removable Bosch battery pack with a lock and key mechanism. (Image Credit: Bosch)

As for the number of packs, some eBikes, such as Juiced Bikes HyperScramber 2, can have dual battery packs to give you an unusually long range. But, understandably, these bikes weigh and cost more.

Electric Bike Batteries & Range

Range, or how much distance you will be able to cover on your eBike on a single charge, depends mainly on your battery capacity. The more Ah and Wh your battery has, the longer you’ll be able to go. The other significant factor is what level of assistance from the motor you use during your ride.

Most electric bikes usually come with three riding modes: throttle, pedal-assist, and manpower. The throttle mode (also known as the pure electric mode) uses 100% motor power to let you move around without any pedaling at all, while the manpower (also known as the cycling mode) means you won’t be using any motor power at all. 

The pedal-assist mode lies in between, that’s you get assistance from the motor but you also have to pedal. Most eBikes have further power levels in the pedal-assist mode to let you select how much assistance you want to get from your motor. 

For instance, you will get very less assistance at lower/ eco modes (e.g. at PAS 1) than at sport/ performance modes (e.g. at PAS 4 or 5).

Now, as you’d probably know, the range of a battery significantly depends on how much assistance you get from the motor. You can endlessly ride an electric bike without draining its battery if you don’t engage the throttle or pedal-assist modes and use just your own pedal power. 

Likewise, you’ll drain your battery more quickly when using throttle than when you use the pedal-assist system. Within the pedal-assist levels, you’ll get more range at lower PAS levels than at higher PAS levels.

Manufacturers are very crafty when it comes to range estimates of their eBikes, so you need to be very careful when making your buying decision. Most range estimates are only true at the lowest pedal-assist level (that requires you to do most of the work), unless stated otherwise. 

Some brands, however, list their throttle and pedal-assist range separately… which kind of gives a more accurate estimate. A few brands, such as Aventon, go so far as to provide a range estimate for each level of pedal-assist (including the top-speed offered by that PAS level) to give you a perfectly accurate picture of what to expect.

Besides the battery capacity and the level of assistance from the motor, here are some more factors that determine your range.

  • Total weight: The more the weight (bike + rider + payload) on the bike, the less would be the range.
  • Type of motor: A mid-drive motor gives you far more range than a hub motor (with everything else constant) due to its super-efficient working mechanism. If you want to explore more on how the hub and mid drive motors differ from each other, check out this in-depth hub vs mid comparison.
  • Type of sensor: Torque sensors are more efficient than cadence sensors due to their high-sampling rate so they give you more range. Read this detailed torque vs cadence explainer to know more.
  • Riding style: Starting/ stopping frequently such as in urban stop-and-go traffic reduces range.
  • Ride speed: Electric bike batteries don’t work efficiently at higher speeds, so you get less range.
  • Width of tires: Thin tires face less rolling resistance than fat tires, so you get more range.
  • Type of terrain: You get more range on flat roads than on hills as you don’t need too much power.
  • Use of gears: Multi-speed bikes give you more range than single-speed bikes due to the mechanical advantage of gears.
  • Age of battery: The charge holding capacity of a battery decreases as it approaches the end of its service life.
  • Other factors: Tire pressure, wind and weather conditions, and even your ride posture impact your range.

While making your decision, make sure to buy the right battery. And by right, I mean just the kind you need. It’s also important because the battery is the costliest component in an electric bike. 

So, you need to accurately determine your needs. If you don’t travel beyond 20-25 miles in a day, you don’t have to buy a costly eBike that gives you 60 miles on a single charge. But if your workplace is too far or you encounter hills in your commute or you haul heavy loads, you’re better off with a long-range electric bike. 

Range estimate + top speed for each level of pedal-assist for Aventon Pace 500. (Image Credit: Aventon)

Charging an eBike Battery: Time & Cost

The charging time of an electric bike battery depends on two factors: its capacity or size (measured in amp hours/ Ah) and the ‘amp’ rating of the battery charger. 

A battery with a larger capacity will obviously need more time to be topped up. As far as the amp rating of the charger is concerned, higher values indicate that the charger can let more current flow through it, so will top up the battery more quickly than the one with a lower amp rating.

Most Lithium-ion batteries on the market today need 4 to 6 hours for a full charge when they’re completely drained. Understandably, a battery that isn’t fully drained will take less time for a full recharge.

 You can easily calculate the charging time your your eBike battery with the following formula: 

Charging time (h) = Capacity of battery (Ah) ÷ Current flow rate of charger (A)

For instance, if you have a 10Ah battery, a 2A charger will need 5 hours to juice it up from a fully depleted state. However, no electrical process is 100% efficient and there’s always a loss of energy due to internal resistance. So, when you account for that loss (say 20%), the actual charge time will come out at 6 hours. 

Using a quick charger (the one that has more current flow rate) will reduce your charging time. For instance, if you use a 4A charger for a 10Ah battery, it will be able to fully top it up within 3 hours!

You can luckily reduce the charging time without using the quick charger. It’s because Lithium-ion batteries follow an inverse exponential charging curve, so you don’t need to wait to top your battery to a full 100%.

Let me explain it in simple words. An Li-ion battery that needs 6 hours to charge fully can be recharged to around 80-90% in 4-4.5 hours… so you don’t need to wait till it’s been fully topped up. Doing so will not only save you time, but increase your battery’s service life… as ‘topping off’ Lithium batteries is proven to reduce their efficiency with time!

If you want to find how much it costs to charge your eBike battery, you can easily do that too. You just need to multiply your ‘Wh’ rating or the energy content (in kilowatt hours) with the cost of electricity in your area. 

For instance, a single full charge for an eBike with a 36V 10Ah (or 360Wh/ 0.36kWh) battery at an average electricity cost of $0.144 per kWh will come out to be $0.052 or 5 cents. Now if you get a range of say 20 miles (32km) for a single charge, you’ll be spending just over 5 cents for traveling 20 miles!

Lifecycle of eBike Batteries

Most eBike batteries have a life cycle of 800 to 1,000 charges. It means you can recharge a battery rated at 1,000 charge cycles a thousand times before it needs replacement. However, a cycle is only counted as one when you charge your battery from 0-100%.

In other words, if you charge your battery while it already has some charge inside it, that won’t count as a full cycle. For instance, if you charge a battery every time it drops to 50%, you’re only using half of its charging cycle per ride, and this battery will last for 2,000 charges (if it was rated at 1,000 full charge cycles).

You can also use the battery charge cycles to determine how much total distance you will be able to cover with a battery during its lifetime. For instance, if you get 20 miles (32km) of range on pure electric power, then a battery rated at 1,000 cycles will take you to 20,000 miles before being out of use.

However, keep in mind that a battery rated at 1,000 cycles can need replacement much sooner, depending on how you take care of it. 

As I said earlier, electric bike batteries come with a battery management system (BMS) for protection against internal/ external threats, but they can lose their efficiency much sooner than their rated life cycle if they’re exposed to extreme temperatures for a prolonged period or if they’re not charged appropriately. They can even burst into fire… as I’ll discuss in the next section.

An electric bike battery exploding into fire. (Image Credit: Reddit)

BMS and Exploding eBike Batteries

Besides packing lithium-ion cells, the battery pack also has a temperature sensor to continuously monitor the temperature, a regulator and voltage converter to keep the current and voltage at safe levels at all times, and a battery management system (BMS) – that’s basically a tiny computer working to ensure safety. 

The BMS shuts down the battery in case it experiences over-heat, over-charge, over-discharge, over-current, short-circuit, or any other kind of internal/ external threat to avoid any damage to the battery cells.

This system is extremely important for the safety of the battery and any damage to it can (in rare cases) lead to your battery bursting into fire. The biggest reason behind lithium batteries catching fire is a damaged BMS that won’t shut down the battery on overheating. 

Besides the faulty BMS, electrical shorting, repeated overcharging, repeated exposure to high temperature, use of the wrong charger, or any damage to the casing such as when battery gets damaged in an accident or due to any reason can also lead to fire ignition in eBike batteries. 

But don’t worry… Lithium batteries catching fire is a rare phenomenon and you don’t need to freak out. As long as you charge, discharge, and use your battery carefully, it will never happen to you. 

How to Take Care of eBike Batteries?

If you want your battery to last for its rated charge cycles without losing efficiency and never experience such horrendous things as catching fire, just follow the following battery care tips and you’ll be good. These tips will also help you get more range per charge.

Charge/ Discharge ‘Shallow’

Instead of charging your battery fully or letting it discharge completely, the ‘shallow’ method of charging and discharging significantly increases its service life. It means you should charge your battery to 90-95% and not the full 100%… and recharge it as soon as you can, and not wait till it has completely discharged. 

A common myth that unnecessarily complicates the life of many riders is that eBike batteries perform the best when they are recharged after they have fully drained. It’s not only untrue, but is also not good for the battery.

All battery manufacturers recommend charging your battery as soon as you can. Samsung, for instance, advises its users to make sure their batteries are never drained to below 20%. The only exception to the ‘shallow’ charge/ discharge regime is when you buy a new electric bike, as a new battery is always recommended to be juiced up to a full 100% before you use it.

Charge Regularly

Just as I said above, the best way to maintain the efficiency of your battery is to charge it as often as you can, preferably after every ride – no matter how short it is. You can even charge it midway whenever you stop at a coffee shop or something.

If you won’t be using your eBike for an extended period or if you have to store your battery for any reason, make sure to never store it when it’s empty – doing that will mess it up, pretty badly. 

Charge it to at least 50% (the more, the better) and store it in a place that’s dry and isn’t too hot/ cold. If you plan to keep your battery stored for a really long time, recharge it every couple of months.

Charge at Room Temperature

Using your battery during freezing winter is fine (you’ll see your range drop a bit, but your cells won’t be damaged). However, it’s not recommended to charge a frozen battery pack. 

If you live in a cold environment, you need to be extra careful about how you charge your battery. Once you’re inside your place, you should give your battery adequate time to warm itself up before you plug it in the socket. 

Never Experiment 

Never use your eBike battery to power any other electrical device or an incompatible eBike. 

Likewise, always use the charger that’s provided with the battery as using an incompatible charger can seriously damage your battery (leading to ignition, in worst cases). It can almost always void the warranty on your battery too.

In case your charger gets lost or damaged, contact the manufacturer to get another unit, rather than trying out something on your own.

Read the Literature

The best way to know how to properly charge and maintain your battery is to read the user manual or the literature that you get with your electric bike, as it always contains detailed instructions about what to do and what not to do.

If you have a query that’s not covered in the instruction manual, you should try to consult the support team of the manufacturer or get guidance from an expert. You can even drop a comment here and we’ll be happy to guide you!

If you want to explore electric bikes, here are the best eBikes for urban use, here are the best ones on Amazon, here are the best options under $1000, and here are the best ones under $500

If you don’t want to buy a new eBike at all, you can electrify your regular bicycle with electric bike conversion kits at an affordable cost, provided that it’s in good shape. With that, I’ll sign off… hope it was an informative read!

Author

  • Frank Gao

    Frank is the owner of eBikeDaily. He moved to Canada from China at 16 and went on to study Mathematics in college. He now lives in Shenzhen (the hub of eBike industry in China) and works in close collaboration with many notable Chinese electric bike brands. A huge eBike nerd himself, Frank can be found riding or testing one – at all times!

Leave a Reply