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All about Batteries for Electric Bikes

Battery size and Range Determination
To determine the true range of an electric bike, a person must look beyond the mileage claims made by the manufacturer.

No Standard Range Calculation for Electric Bikes
There is no National or International standard for Electric Bike range calculation, as there is with EPA car mileage ratings. Each manufacturer makes up their own mileage claim. Ranges for bikes vary widely, depending on speed and how much the rider is pedaling. An electric bike has an infinite range, if the rider is pedaling without the motor. The only true way to determine the range of electric bike is with an actual road test.

Three Factors Determine the Range of Electric Bike

Factor #1 Size Of Battery
In general, the  range of an electric bike is directly proportional to the size of the battery. A bike with a bigger battery will go further. This is an important fact to remember when researching bikes. (See below on how to compare battery sizes)

Factor #2 The Terrain
The second  factor that greatly affects range is the terrain, Just as with a car, an electric bike will not go as far if you are climbing hills versus riding on the flats.

Factor #3 Efficiency of Motor Drive System
The third factor in determining range is the type of motor drive system used. The Optibike Motorized Bottom Bracket is over three time more efficient when climbing hills than a hub motor. This means the Optibike it will climb further with the same size battery than a hub motor bike.

The Battery is like a Car’s Gas Tank
The size of the battery is analogous to the size of a car’s gas tank. A bigger battery, like a bigger gas tank, will go further. The size of a gas tank is measured in gallons,  the size of a battery is measured in watt-hrs. (amp-hrs are also used, but they do not provide the whole picture as they do not include the voltage of the battery pack).

Battery current is a analogous to the amount of gas flowing into your carburetor. As your car flows more gas, your tank empties quicker.  When you draw more current from your  battery, your battery empties faster.

How Battery Capacity is Measured
Batteries are  rated in either amp hours or watt-hours.  A20-amp hour rated battery can produce 20 amps for one hour and it’ll be drained.  A 10-amp hour battery can produce  10 amps for one hour. That’s how they’re rated.  But it’s not the whole story because the entire amount of energy you have in your battery is the amp hours times the voltage of the pack.  So a 12-volt pack at 10 amp hours is not the same as a 36-volt pack at 10 amp hours.  A 36-volt pack at 10 amp hours has 3 times the energy of a 12-volt battery at 10 amp hours because 36 volts is 3 times 12 volts.  So the standardized way to look at it would be in watt-hours, and watt-hours are actually volts times amp hours gives you watt-hours, which is energy.

Energy and  Power are Different
Many people confuse energy and power. Horse Power is power, not energy. Horsepower accelerates you,  but energy lets you go the distance. (Energy is the amount of fuel in your tank) Batteries with high power ratings can accelerate you quickly, but  usually have low energy ratings, resulting in short distances traveled. Energy is watt-hrs and energy keeps you going for the distance. In an electric bike, energy is more important than power.

The Simple Way to Calculate Range
As a general rule, look for a bike where the motor capacity rating in watts is equal to the battery capacity in watt hrs. (Many battery packs are rated in amp hrs. It is easy to convert this to watt-hrs by multiplying the voltage of the pack times the amp hrs.)  If they are equal, the bike will run for one hour at the rated motor power. The true range of the bike can then be easily found by multiplying the speed of the bike by one hour.

Jim Turner is the Inventor and Founder of Optibike Electric Bikes