E-Bike Batteries – Capacity, Range, Charging Time & More

E-Bike Batteries – Capacity, Range, Charging Time & More

March 10, 2021

What would an e-bike be without a battery?
Right, an overweighted bicycle!

 

An e-bike battery is the heart and the energy source of the bike and logically also the most expensive component of the entire vehicle.
And not without reason, after all, the battery has a lot to perform and must in turn be able to take a lot! No matter what the weather, the load or the gradient – the battery must always provide enough energy to get us and our passengers from A to B relaxed and sweat-free. The journey is often the destination and we like to take the longer way home.



The requirements for this high-tech construct of lithium-ion cells are complex:

  • When starting from a standstill, the battery must provide a lot of power in the short term, so it should first supply the drivetrain with energy and react immediately to pedaling.
  • Within the assistance spectrum, it is challenged in that it must provide energy for as long a period as possible.
  • Ideally, the battery capacity should be inexhaustible and provide energy without restriction both in heat and at temperatures well below 0° C.
  • Of course, the charging process should only take the blink of an eye, and the battery should last forever.

This roughly represents the requirement that the e-bike battery should master from the user's point of view! Nevertheless, a high performance and life expectancy requires the correct handling of this complex component.

The following chapters provide an insight into the various characteristics of the e-bike battery and enable a better understanding of its requirements and possibilities.

 

Capacity & Range

Simply put, the capacity of a battery describes its "size" and thus allows a possible range to be derived. The unit of capacity is given in ampere-hours (Ah), which in turn can be converted into the more common household quantity of watt-hours (Wh) by means of the voltage in volts (V):

Capacity (Ah) x Voltage (V) = Energy Unit (Wh)

14.25Ah x 48V = 684Wh or 20.4Ah x 48V = 979,2Wh so almost 1kWh!

We currently offer the following battery types & capacity models, which are limited to two different package standards (Silverfish & Hailong) and one soft pack variant:

  • 14.25Ah 48V Silverfish Battery for UNI MK/Bobber/Swing (ca. 80km / 50 miles)
  • 20.4Ah 48V Silverfish Battery for UNI MK/Bobber/Swing (ca. 100km / 62 miles)
  • 13.8Ah 48V Hailong Battery for UDX (ca. 60km / 37 miles)
  • 17.25Ah 48V Hailong Battery for UDX (ca. 80km / 50 miles)
  • 14.0Ah 48V Custom Softpack Battery for UNI Boost (ca. 60km / 37 miles)

The battery sticker tells you more about the characteristics of your battery.

 

A battery's range depends very much on vehicle type/weight, terrain, load, tire pressure & type, wind and road conditions as well as other factors and can therefore vary greatly.

Especially in wintertime with low outside temperatures, the capacity/range of the battery can be noticeably affected, but this is normal for lithium-ion batteries and returns to normal when temperatures rise.

Likewise, riding style plays a decisive role in the possible range. Anticipatory riding to avoid unnecessary braking actions and to minimize start & stop maneuvers (e.g. in city traffic) or smart riding allow a higher range – varying the pedal assist level (e.g. when going downhill), extensive use of the mechanical gear shift to relieve the load on the electric drive train and other actions have a decisive influence on the range.

Our range figures are based on ideal conditions, i.e. low payload, low assistance level, no start & stop traffic, level asphalt surface, adequate tire pressure to minimize rolling friction, outside temperature of 24°C, adequate addition of muscle power, no thumb throttle, max. speed of 25km/h.

The range record with the 20.4Ah battery is 155km!

 

Finally, two short rules of thumb for rough orientation:

  • 9Wh consumption per 1Km riding distance with pedal assistance
  • 18Wh consumption per 1Km riding distance with (thumb) throttle

 

Charging Time

The charging time varies depending on the remaining charge level, battery size/capacity/temperature and the charging current normally between 4 and 8 hours, possibly longer when charging new bike batteries for the first time.

The standard chargers have a charging current of 2A (amps) and mostly use a DC plug (UDX) or an XLR plug (UNI MK/Bobber/Swing) common in the audio sector.

Fast chargers on the other hand promise a shortened charging time thanks to higher charging current, e.g. 3A to 5A instead of the conventional 2A.

 

 

In principle, the battery charging time can be calculated as follows (completely empty battery or one full charging cycle):

h = hours | Ah = ampere hours | A = ampere

Charging time (h) = capacity of the battery (Ah) / charging current (A) * 1.3 (electr. work)

Example:

14.25Ah / 2A * 1,3 = ca. 9h 15min

20,4Ah / 2A * 1,3 = ca. 13h

20,4Ah / 5A * 1,3 = ca. 5h 20min

 

Lifetime & Charging Cycles

In the case of the battery, we do not talk about a range limit until "the juice runs out", but about the total number of so-called charging cycles that it has undergone.

A charging cycle describes a charging process of a completely empty battery (0%) up to the completely full charge level (100%) including its complete discharge.

 

Examples:

A half-full battery that is charged and discharged again has consequently only used "half" a charge cycle, a 75% full battery logically only a quarter of a charge cycle, etc. - here we speak of partial cycles.

If you have 20% of the full battery volume available and charge the battery to 70%, use the battery again to 20%, and do exactly the same again, a complete charge cycle is reached and a new one begins.

 

It is therefore the total number of charges or full charge cycles that add up with each additional charge.

The battery manufacturer specifies a number of 800 to 1000 charging cycles until the battery has a remaining capacity of 80%. This means that the battery is still usable and provides up to 80% of its original capacity and range. If you map this to a period of normal, regular battery use, you're looking at about 2-3 years of life. In addition to common wear and tear, batteries age over time (cell aging), regardless of use and care. Unused as well as regularly charged and well maintained batteries lose about 4% of their storage capacity per year.

Over time, the battery loses "power", it decreases with increasing use, which is perfectly normal. So what can you do to extend the battery's life?

The next section will tell you.

 

Extend Lifetime

On the Internet, you can find a lot of tips and advice on how to significantly extend the life expectancy of your battery - sometimes the statements contradict each other and unfortunately confuse more than they help. We have therefore briefly summarized the best tips around battery maintenance, care and storage.

The following points can positively contribute to the life expectancy of your e-bike battery:
  1. Before normal use, calibrate the new battery, i.e. fully charge and discharge it the first 2-3 times.
  2. Afterwards, do not fully charge and discharge the battery during normal use.
  3. Store the battery at room temperature (between 15 - 20°C) and away from direct sunlight in a dry place.
  4. In case of longer periods without use, check and charge the battery regularly (approx. every 30 days) so that the charge level is constantly between 30% and 60%.
  5. Only use the appropriate charger for charging and avoid using fast chargers if possible.
  6. When cleaning the bike, remove the battery and carefully wipe it with a cloth - do not use any cleaning agent. Also keep the battery terminals/connectors clean.
  7. Never open the battery on your own (e.g. in case of defect/failure) but contact a specialist or the manufacturer directly.
  8. A battery that was thought to be dead can be reanimated under certain circumstances. Here a battery analysis as well as if necessary an exchange of weak cells comes into question - contact a battery specialist or the manufacturer for this. There are also many online services that service and refresh batteries.
  9. Deep discharged batteries do not have to be written off directly, but can possibly be revived with the help of special chargers and know-how. Speaking of deep discharge - what is it actually all about?

 

Deep Discharge, Self Discharge & BMS

Deep discharge is caused by excessive current consumption and manifests itself in the almost complete exhaustion of the battery charge capacity, which falls below a certain voltage level. This can be harmful to the battery and should therefore be avoided as a matter of urgency or prevented in advance. To detect such a deep discharge, the output voltage must be measured using a volt/multimeter.

A deep discharge is when the charge level of the battery falls below 20% of its capacity, i.e. below the final discharge voltage or the minimum voltage limit. This can result in various damages. For example, if cells are connected in series, they can even be reversed in polarity due to a deep discharge. The damage can occur after just one deep discharge. If a battery is not used for a longer period of time, the cells can self-discharge – a whole 0.5% to 1.0% of the battery's capacity per month.

Common protective measures or circuits installed in rechargeable (lithium-ion) batteries are so-called Battery Management Systems (BMS), whose task is to monitor and control the balanced charging and discharging of the cells or cell packs and thus prevent overcharging. These systems, in the form of circuit boards, store important data such as the number of charging cycles to date, the current charge level and the expected remaining service life, and can be read out by the manufacturer or a specialist using appropriate analysis tools.

Battery Storage & Hibernation

What is the best way to store my battery, e.g. during the winter break?

We have already learned that the battery loses capacity not only during use, but also during storage - in the form of the previously mentioned self-discharge.

How you store the battery unit will also affect the discharge rate. Even short-term storage at high or very low temperatures can already damage the battery irreparably, so avoid temperatures below -10 °C and above 40 °C whenever possible. Some manufacturers already warn that even 4 hours at temperatures between 40 °C and 60 °C can have a negative effect on battery life and such temperatures are reached faster than expected – in the trunk of your car, in the winter garden or even in direct sunlight. At the other end of the scale, 20 hours at temperatures of -20 °C can cause equally irreversible damage. Your battery should be stored at a temperature between 0 °C and 20 °C in a completely dry place, but away from flammable materials. All manufacturers agree that the optimal storage temperature is a constant 10°C, as this slows down degradation processes and reduces the aging rate of the battery.

How do I bring the battery back from hibernation to use it?

Even after extended storage, for example in winter, it is possible to simply plug the battery into the bike and ride without recharging. Modern lithium-ion cells have no classic memory effect, so lithium-ion batteries can be charged at any point in their state of charge without causing damage or reducing capacity - regardless of interruptions and charging time. To gently wake the battery from hibernation, it's best to fully charge it once and then run it down again. Only then should you fully charge it again. This procedure helps the battery management system to calibrate and calculate the battery capacity.

 


We hope that this article gives you a helpful insight into the battery topic of e-bikes as well as a better general understanding of lithium-ion batteries.

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