A Kalkhoff Pedelec is a lot more than simply bolting a motor onto a great bike. Their electric-assist bicycles utilize a brushless DC motor system that is lightweight, precisely-controlled, efficient, low-maintenance, and reliable. The Panasonic drive system is center drive, meaning that it's designed to be in the middle of the bike for a low center of gravity, stability and an easy integration with the drivetrain. The drive unit is more than just a motor; it also has a torque sensor and controller unit as well - all in the weatherproof casing, surrounding the motor. The torque sensor and the controller senses how hard you're pedaling and adjusts how much assistance the motor gives you through the drive sprocket.
E-bikes use rechargeable batteries, electric motors and some form of control. Battery systems in use include sealed lead-acid (SLA), nickel-cadmium (NiCad), nickel-metal hydride (NiMH) or lithium-ion polymer (Li-ion). Batteries vary according to the voltage, total charge capacity (amp hours), weight, the number of charging cycles before performance degrades, and ability to handle over-voltage charging conditions. The energy costs of operating e-bikes are small, but there can be considerable battery replacement costs. The lifespan of a battery pack varies depending on the type of usage. Shallow discharge/recharge cycles will help extend the overall battery life.
I tested the Sduro 8.0 towards the end of last year (there's a new range out for 2018) and was surprised by its nimbleness. You expect e-bikes to be less maneuverable than their acoustic predecessors, but, pelting down some bespoke forest paths near Pedal & Spoke in the Surrey hills, I found I completely forgot that there was a box of electronic EPO on my frame. Partly, that's because the battery is cleverly integrated into the frame to decrease drag; mostly, it's because the suspension is soft and the steering nimble, much like a normal mountain bike.
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).