Electric Bike battery

Electric Bike Battery Basics & Range Estimating Tool

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You’ve made the jump into the electric bike world with a brand new motor. Now you just need a electric bike battery, or you want to upgrade for longer range. There are so many different types, how do you choose?

Knowing which kind of Electric bike battery to choose can be difficult. Batteries vary from weight, size, capacity, and configuration. It might not be clear which type will be best for you at first glance.

The type of battery you choose needs to depend on also conditions, and riding style. Will you be going short distances or long? Up hills or mostly flat? They reflect on what kind of riding, bike and effort you will be going through. You need to think of the overall weight of the bike as well. Finding answers to these questions will help guide you to the ideal battery.

Luckily, we’re here to assist you in selecting the Electric bike battery that will be the best for your needs.

Electric Bike Battery Math

To get a better understanding of what to expect from these batteries, you need to know a bit of math. First, it’s essential to understand how to calculate the total watt-hours you can get from a battery.

How to calculate total watt-hours?

Watt-hour (Wh) is a number get from multiplying the battery amp-hours (Ah) and the voltage (V). For example, a 48V / 10 Ah battery is 480 Wh. In very general, it could be estimated that you can get about 1.6 km for every 20 Wh. So from a 500 Wh battery, you can expect to get 40km out of range.

Of course this depends on weight, motor and how you ride, but in general, that’s about what you can expect. If you have a high power (wattage) motor, you can burn through energy much faster but also travel quicker. Lower power (wattage) motors might be more efficient with pedaling in the urban environment.

Controller

One other important thing to note is what your controller can handle. You need to be sure that your controller is compatible with certain voltage of battery. As they are rated 24V, 36V, 48V and 52V commonly in electric bike system. Also the current (A) output is limited by the controller to keep the temperature down. Let’s say when you pull out from a steep hill and try to accelerate, the controller will limit the current (A) at the maximum. So the controller won’t get burnt out easily. 

In terms of voltage, when inspecting the data sheet of most common 18650 lithium-ion cells then we can find out that they got a nominal voltage (3.6V or 3.7V) and maximum charging voltage (4.2V). Some of cells rate minimum discharging voltage at 2.5V but they have almost no capacity left when they got discharged to 3 volts because of the voltage drop. That means we got a voltage range of 3 volts to 4.2 volts per cell. So for example, if we make 13 cells in series that provides a 48.1V battery pack with a range from 39V to 54.6V.

The number of paralleled cells will decide the capacity and discharge rate. For example, 2 Samsung 25R cells with 2500mAh and 20A discharge rate can be paralleled to double the capacity and discharge rate into 5000mAh and 40A. 

If you are looking for a 48V 10Ah battery constructed by 2500mAh cells, it can be listed as 13S-4P. And a 13-series-4-parallel pack indicates 52 pieces of battery cells that you can have an idea of general weight. So now we have a basic idea about battery voltage (V), current (A), capacity (Ah) and power (W) to pick up battery more precisely.

Useful tool to make life easier

Getting struggle with math and calculation? Don’t worry it is 21st century now! Bosch E-bike built a great website to help figuring out the estimation without any effort. All we need is just simply click into the ‘eBIKE RANGE ASSISTANT’ webpage and it is almost done.

Electric Bike battery

First of all, there are a few options to set up in unit and rider’s details:

  1. Unit: mile or kilometre
  2. Total weight: add up rider, bike and luggage in total
  3. Cadence: how fast do you pedal? Can get a roughly number by checking the stickman’s demonstration. Average cyclists have a cadence of about 60 RPM

Secondly, swap to the ‘eBike’ tab next to the ‘Rider’ tab, there are five sections to set up:

  1. Drive: Bosch motors could be referred to different mid-drive system by checking the maximum torque and wattage. For example, A 500W Tongsheng is similar to ‘Performance Line Speed’; a 250W Bafang is similar to ‘Performance Line CX’
  2. Battery: by multiplying the V and Ah of your battery, the number you get can be referred to Bosch batteries’ model number. For example, a 48V 10Ah battery is similar to ‘PowerPack 50’. The biggest option goes to 1250Wh with ‘DaulBattery’’PowerTube 625’
  3. Type of bicycle: very comprehensive selections of bikes; choose ‘eMTB’ for full-suspension and ‘MTB’ for hardtail
  4. Tire tread: several types to choose
  5. Shifting system: derailleur or internal hub gear.

Next, move on to the ‘Environment’ tab to set up your riding conditions:

  1. Terrain: how frequent to ride uphill?
  2. Surface: road surface condition affects efficiency
  3. Wind conditions: how stormy wind are you heading?
  4. Season: temperature affects the battery performance
  5. Starting up: how frequent to stop in traffic?

Finally, set your riding pace through:

  1. Average speed: divide the distance by travel time then you get the average speed
  2. Riding mode: pedal assist level
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