How far can I go on one charge?
How far can I go on my battery?
There is a lot of technical jargon in the electric bike world, and we think that scares many people off. But some of the jargon has important ramifications, like the term "amp hours" (often written as Ah or AH). Amp hours is a measure of the capacity of a battery, expressed as current (amps) times time (hours). A battery with 10 Ah can run twice as long as a battery with 5 Ah. The most common size for e-bike batteries is 10 Ah, because these are compact and light, but give enough range for most uses in and around towns. The amp hour rating of a battery is a good indication of the range you will be able to travel on one charge, but this range is also determined by how much you are using the electric-assist, how much weight you have on your bike, how many hills you have and even conditions like headwinds. Just think about riding without electric-assist. You are going to be needing more energy if you have a hilly ride with a headwind or are carrying 100lbs on your cargo bike than if you are cruising on flat lands. So the range of a battery is always, a range!
Here is a rule of thumb that can be used to determine your battery range. Calculate the overall number of watt-hours (energy) available for use in your battery by multiplying the voltage times the amp hours. For example, in a 36V 10Ah pack, this would be 360 watts. Then divide this by the number of watt-hours used per mile. From personal experience, with a 36V system over rolling terrain, a conservative use of power (such as just using assist on the hills) is about 10 watt-hours per mile, while a liberal use of power (full throttle most the time) is up around 20 watt-hours per mile. Using this rule of thumb, this battery pack would give you between 18 (=360 / 20) and 36 (=360 / 10) miles of range on one charge. For a 48V system, it is easier to use more power per mile because there is more power available, so the number of watt-hours used per mile could go be more, or if your ride is mostly uphill, your use per mile could be more.
In real world use, the amount of total watts available from a battery is slightly less than the calculated total because when the battery is getting low, the battery will shut itself off to prevent damage from low voltage. Different battery chemistries have different discharge characteristics that effect what the actual capacity is. For lithium and nickel batteries, you can get about 90-95% of the rated capacity out of the battery before the voltage drops too low. For lead acid batteries, you only get about 60-70% of the rated capacity. So a 36V 10Ah lithium battery will give you as much range as a 36V 13Ah lead acid battery.