While the motor may be the source that actually propels an electric vehicle, the battery pack is its virtual heart and soul. If you’re in the market for a new or used EV, you’ll want to pay attention to the battery’s specs, and be aware of other aspects that will ultimately affect its performance.

Electric vehicles use lithium-ion batteries of various design, similar to those used in cell phones and laptop computers, only on a much larger scale. Lithium-ion batteries have a high energy density and are less likely than other types of batteries to lose their charge when not being used.

An EV’s battery capacity is expressed in terms of kilowatt-hours, which is abbreviated as kWh. More is better here. Choosing an EV with a higher kWh rating is like buying a car that comes with a larger gas tank in that you’ll be able to drive for more kilometers before needing a “fill up”. But be aware that because of the way EVs work, you’ll never actually have access to the full battery capacity. That’s because the car’s management system prevents the battery from either becoming 100 percent fully charged or 100 percent discharged to preserve its efficiency and extend its usable life.

Battery capacities of current EVs range from a mere 17.6 kWh in the Smart EQ ForTwo with a range of just 92kilometers, up to 100 kWh in the Tesla Model S and Model X that can run for over 480 kilometers before needing a charge.