Voltage is a force that makes electricity move through a wire. It is measured in Volts (V). Typical Li-ion cells will be around 3.7V.Typical ebikes are designed to run on 24, 36, or 48 Volts, so a number of cells have to be series connected into a 'battery' that has the desired net voltage. For example, a 36 V battery is formed by 10 Li-ion cells connected in series to one another.
Electrical current is electrical charge in motion. So it is the electricity moving in a wire. It is measured in Amperes (Amp or A).
Watt Is a unit of power defined as 1 joule per second. It can be used to express the rate of energy conversion or transfer with respect to time. To put it into perspective, a labourer working for 8 hours straight will have an output of approximately 75 Watts.
As you draw current from the battery pack, the voltage will very slowly decrease until the cells start to go flat and then the voltage will plummet. The time that the battery lasts for is directly related to its capacity, measured in amp-hours (Ah). For example, a battery that can deliver 1 amp for 1 hour has a capacity of 1 Ah.
The figure that matters most when comparing how far a given battery pack will take you is not the amp-hour capacity but the total energy stored in watt-hours. The watt-hours stored in a battery pack is approximated by taking the actual amp-hours and multiplying it by the battery pack’s voltage.