How much range suitable for you ?This is the most important thing you should know before buying an e-bike.
Most consumer e-bikes target a 20-mile range. The range depends not only on the voltage and wattage of the bicycle, but also on the weight and terrain of the rider. Heavy people on muddy roads will have less range than skinny people on sidewalks.
The battery capacity of electric bike is in amp/hour. The bigger the battery is, the more expensive it is. Usually the range of electric bikes ranges from 8AH to 20Ah (on most specifications, AH = ampere/hour). So for an average rider, you want something similar to a 24 volt 8AH battery connected to a 300 watt motor for a comfortable 20-mile electric bike.
If you have money to spend and need speed, add all 3 numbers and you can have an electric bicycle that weighs 80 miles an hour and weighs 1 ton. So basically what you need to know is that the amp/hour is the capacity of the battery, the voltage is the acceleration (such as the torque of the car), and the wattage is the power and speed (like the horsepower on the car).