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Electric Bike Batteries – A General Overview

It is important to remember that the battery not only gives a rider range it also gives the motor sufficient power to propel the bike up hills when the assistance is most needed. The higher the battery Voltage the more power can be sent to the motor. The larger the capacity of a battery (Ah) the longer the battery will operate at its most efficient voltage, giving a rider maximum hill climbing capability.

When choosing an electric bike it is worth doing this simple calculation; multiply Volts (V) by Amp hours (Ah) in the battery specification to calculate the number of Watt hours (Wh) available. Simply put, the more Watt hours you have, the more capacity will be available, thus the battery will take longer to discharge, enabling the bike to travel further.

A 37V x 16Ah (592Wh) battery has 32% more capacity than an 37V x 11Ah battery (407Ah). Therefore the range of a bike with a 592Wh battery is more than 30% better than the same bike with a 407Wh battery installed.

Examples

37V x 16Ah = 592Wh            Approximate range 65 miles*

37V x 11Ah = 407Wh            Approximate range 45 miles*

36V x   9Ah = 324Wh            Approximate range 35 miles*

Most electric bikes now use Lithium batteries, with either polymer or solid cells. Lithium batteries will normally last between 700 and 1000 full charge/discharge cycles, if used and cared for correctly. Some electric bicycles use lead acid batteries, which have the advantage of being less expensive, however they are heavier and larger than lithium batteries and have more limited charge/discharge cycles available before the battery capacity becomes to small for effective use.

Lithium batteries are now up to 90% recyclable.

Smaller capacity batteries have the advantage of being cheaper and lighter weight.

Larger batteries are often more cost effective as not only will they hold more power for longer journeys, they tend to last longer than smaller batteries. They will also assist an electric bicycle for many more miles during their lifetime.

Maximum range could fall as low as 50% of these figures depending on rider weight, power settings, climatic and road conditions. If the bike is used on the throttle only the range will be reduced even more significantly.

* These ranges were achieved by a rider weighing 11.5 stones on a flat dry surface with a air temperature of 10 degrees Celsius with some stopping.

Battery safety

Never attempt to charge a battery in temperatures of less than 2 degrees Celsius, this is dangerous and could cause fire.

Only use the charger supplied with the bike or a replacement from the bike manufacturer, using the incorrect charger is dangerous and could damage the battery or cause fire.

If a battery case has been damaged, do not continue to use it unless it has been checked by the supplier or manufacturer and they have declared it safe to use.

If a battery is paired an with intelligent charger that will automatically switch off when the battery is fully charged it is safe to leave them to charge overnight, providing the air temperature is above 2 degrees Celsius. If you are not certain that the battery/charger set up you have has this facility do not leave a battery on charge overnight.

 

Battery care

It is important that all lithium batteries are well cared for to achieve optimum performance. Many batteries now 

are equipped with a device that will enable a manufacturer to see exactly how the battery has been used.  If a battery has not been looked after according to manufacturer’s instructions it may not be covered by their warranty.

The life of the Battery will depend on the quality of the cells used to construct it. A battery with high quality cells, kept well maintained and used correctly according to the manufacturer’s instructions should give good service for more than 3 years, this is a key point when making the purchasing decision due to the high cost of replacements.

Battery maintenance advice

It is no longer necessary to completely discharge and recharge modern lithium batteries. It is recommended that batteries are always recharged when possible even after a short journey; this keeps the battery healthy and always available for longer journeys.

Important

Never leave a battery completely depleted or drained; this will prevent the battery voltage from dropping below safe levels, which can cause irreparable damage to the cells.

During long periods of storage and non-use keep the battery about 2/3 full and top up for two hours every eight to twelve weeks.

For optimum power and range keep battery in a Dry/Warm room above 15 degrees Celsius.

A lithium electric bicycle battery will take between 2 and 6 hours to charge depending on the capacity of the battery and the Amperage of the battery charger.

Range

Electric bicycle manufacturers will often advertise the very best ranges achievable, from their battery and bike set up, what is achievable depends on the rider and how they use the battery.

Ranges will be reduced massively depending on many variables. A 600Wh powered bike ridden in perfect conditions is able to return a range of over 100 miles, the same bike with soft tyres and a heavy rider using a throttle, carrying full panniers, in wet, cold, off road conditions could return as little as 15 miles.

A list of the most significant factors that will influence the range the bike will travel before the battery is discharged is as follows:

Tyre pressures

Keep tyres at the correct pressure as recommended on the tyre wall. As an example, a pedelec’s tyres 1 bar or 14.5psi below the correct tyre pressures will reduce range by as much as 50%.  Incorrect tyre pressure is the main culprit for reducing range, and can cause spokes to become loose and break.

Throttle

Use of a full independent throttle can reduce range by as much as 80%.

Gears

Staying in the correct gear is important to maintain maximum range, especially on a pedelec fitted with a centre motor.

Hi levels of assistance

The higher the assistance level chosen the lower the range of the bike will be, this again can reduce the range by up to 70%

Weight

Not only the weight of the rider but any luggage being carried or towed, towing is not recommended by most electric bike manufacturers.

Wind resistance           

The rider’s stance, clothing and wind direction make a difference.

Air temperature

Cold conditions will reduce range by up to 30%.

Road conditions

Riding on a smooth flat dry road will return a far higher range than riding on gravel or grass.

Hills

Less power will be used on a flat road than in hilly country.

Battery age

As batteries get older they start to lose their capacity. A two year old battery if used every day may lose 20 – 30% of it’s capacity.

Stopping and starting

Every time you brake you take energy out of the bicycle and starting from stand still uses very much more power than cruising at a constant speed. Therefore city riding with all the stops and starts will return lower ranges than riding on the open road.

David Miall, Amps Electric Bikes


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