Electric Motor. Having a battery that will last long is just one piece of the puzzle. The electric motor should be powerful enough to move the bike on flat surfaces without any problems and to overcome some low-steep slopes. It will help you out on steeper slopes, it won’t let you down. If the motor or “the engine” is more powerful you’ll be able to accelerate faster and to reach a higher momentum. This will allow you to reach your destination faster and without you getting tired.
After you decide which style of e-bike you want, consider the class. In the US, there are three classes defined by the type of assist and how fast the motor will propel you. Most electric bikes sold are class 1 or 3. Class 1 bikes have a motor (max 750w) that assists while you're pedaling, up to 20 mph. Class 3, also known as “speed pedelec” can also have up to a 750w motor, but it can assist you up to 28mph. Both of those are allowed in most states and cities without license. Class 2 have throttles that don't require you to pedal to get a boost. They're allowed on most streets, bike lanes, and paths, but less popular than the other classes and not covered much here (because we still love to pedal and the greater distances pedal assist bikes can cover).