Battery Basics: kWh, Range, and Efficiency (mi/kWh)

Three numbers explain almost everything about how far your EV goes and how much charging costs: battery size, range, and efficiency. Once you see how they relate, range and charging stop feeling mysterious.

Battery size: kWh

Your battery's capacity is measured in kilowatt-hours (kWh) — the total energy it can store. Think of it as the size of your "tank." A 60 kWh battery holds less energy than an 80 kWh one, all else equal.

But kWh alone doesn't tell you range, because two cars with the same battery can go different distances depending on efficiency.

Efficiency: miles per kWh

Efficiency is how many miles you get per kWh of energy — your "miles per gallon" equivalent. A car that does 4 mi/kWh is more efficient than one that does 2.5 mi/kWh.

Range ≈ Battery size (kWh) × Efficiency (mi/kWh)

So an 80 kWh battery at 3.5 mi/kWh ≈ 280 miles of range. The same battery at 2.5 mi/kWh ≈ 200 miles.

Range: the headline number

Range is the result of capacity × efficiency, usually quoted as an EPA estimate under ideal conditions. Real-world range varies with speed, temperature, and terrain (see how weather, elevation, and speed affect range).

Why efficiency matters for cost

Efficiency also drives your cost per mile. At the same electricity price, a more efficient car uses fewer kWh per mile, so it's cheaper to drive. That's why efficiency, not just battery size, determines how economical your EV is. See how much it costs to charge.

Reading your car's display

Most EVs show a live efficiency figure (mi/kWh or kWh/100mi). Watching it teaches you a lot:

• Highway speeds drop efficiency (drag).
• Gentle driving and moderate climate use raise it.
• Cold weather and heating lower it.

Use the numbers for planning

When you know your battery size and your real efficiency, you can estimate range for any trip and know how much energy a charging session will add. For example, adding 50 kWh at 3 mi/kWh ≈ 150 miles. That's the same math a trip planner uses.

ChargeScout factors your charge and route into trip planning so you don't have to do the arithmetic, but understanding kWh, range, and efficiency makes every charging decision clearer. For charging speed specifics, see how charging speeds work.