What size is that battery? How much 'juice' does a battery hold? The amount of electricity held by a battery is very directly related to the speed and/or range you can get with that battery. While you can think of a battery as being like a "fuel tank" it doesn't behave like the gasoline tank on a car or motorcycle. A battery weighs the same regardless of whether it's fully charged or fully discharged. This means you can't do a simple measurement like weight to tell when you're running low on fuel.