EV Battery Explained: Capacity, Range, and Degradation

When you buy an electric vehicle, the battery isn’t just a component-it’s the heart of the whole system. But most drivers don’t really understand what’s going on inside that big pack under the floor. What does EV battery capacity actually mean? Why does your range drop in winter? And why does your 2022 Tesla seem to lose a few miles every year? Let’s cut through the marketing and talk about what really matters: capacity, range, and degradation-three things that decide how long your EV will last and how far it can take you.

What Is EV Battery Capacity?

Capacity is measured in kilowatt-hours (kWh). Think of it like a gas tank, but instead of gallons, you’re filling it with electricity. A Nissan Leaf might have a 40 kWh battery. A Ford F-150 Lightning has a 98 kWh battery. That number tells you how much energy the battery can store.

But here’s the catch: that number isn’t what you actually drive on. The EPA adjusts it for real-world conditions-cold weather, highway speeds, climate control use, and even how you drive. So a car with a 75 kWh battery might only show 240 miles of EPA-rated range. That’s normal. It’s not lying. It’s just being honest about real life.

Higher capacity doesn’t always mean better. A 100 kWh battery in a small car like a Mini Electric would be overkill and heavier, hurting efficiency. The best EVs match battery size to the vehicle’s purpose. A city commuter doesn’t need 90 kWh. A long-haul truck does.

How Range Works (And Why It Changes)

Range is the distance your EV can go on a full charge. But it’s not fixed. It changes with temperature, speed, terrain, and even tire pressure.

Cold weather is the biggest range killer. At 20°F, you can lose 20-40% of your range. Why? Cold batteries don’t move ions as easily, so they can’t deliver power as efficiently. Plus, you’re using more energy to heat the cabin-something gas cars don’t need to do because they waste heat from the engine. EVs have to create all their heat from scratch, and that draws power directly from the battery.

Highway driving at 75+ mph also cuts range. Aerodynamic drag increases exponentially with speed. Going from 65 mph to 75 mph can cost you 10-15% more energy. That’s why your EV’s estimated range drops when you turn on cruise control at 80 mph.

And don’t forget accessories. Heated seats? Fine. Heated steering wheel? Not a big deal. But turning on the cabin heater, defroster, and seat warmers all at once in winter? That’s like running a small space heater inside your car. It adds up fast.

What Is Battery Degradation?

Degradation is the slow loss of battery capacity over time. It’s natural. All lithium-ion batteries do it. But not all EVs degrade the same way.

Most EV batteries lose about 1-2% of their capacity per year under normal use. That means a car with a 250-mile range when new might drop to 230-240 miles after five years. That’s not a dealbreaker. It’s expected.

But some drivers see worse. Why? Three big reasons:

• Fast charging too often-Using DC fast chargers daily, especially in hot weather, speeds up wear. It’s fine once in a while, but daily use? That’s like running your phone on 100% charge all the time.
• Always charging to 100%-Lithium-ion batteries last longest when kept between 20% and 80%. Many EVs let you set a max charge limit. Use it. If you don’t need the full range for your daily drive, charge to 80%.
• Leaving the battery at 100% for days-If you plug in your EV and forget it for a week, the battery stays under high stress. That’s worse than driving it hard.

Studies from the Idaho National Laboratory tracked over 1,000 EVs. They found that drivers who charged to 80% and avoided fast charging daily lost only 0.8% per year. Those who charged to 100% every time and used fast chargers daily lost 2.5% per year. That’s a huge difference over five years.

How to Check Your Battery Health

Most EVs show battery health in the dashboard. It’s usually called “State of Health” or “SOH.” A brand-new battery is 100%. After 100,000 miles, 90-95% is normal. Below 80% is when manufacturers often start offering warranty replacements.

Here’s how to check it yourself:

1. Charge the battery to 100% (if your car allows it).
2. Drive until the battery is around 10-20%.
3. Look at the estimated range shown on the screen.
4. Divide that number by the original EPA range listed in your owner’s manual.

Example: Your 2023 Hyundai Ioniq 6 had a 361-mile EPA range. Now, at full charge, it shows 310 miles. 310 ÷ 361 = 0.86. That’s 86% state of health. That’s still great.

Some apps like TeslaFi or PlugShare can pull this data automatically. But you don’t need them. Just do the math once a year.

What Happens When the Battery Degrades Too Much?

Most EV manufacturers guarantee the battery for 8 years or 100,000 miles-whichever comes first-with a minimum of 70% capacity. If your battery drops below that, they’ll replace it.

But here’s the real question: Do you need a replacement?

If your range dropped from 250 to 180 miles, you might need to rethink your daily commute. But if you only drive 30 miles a day, 180 miles is still plenty. Many people keep driving for years with degraded batteries. You don’t need 100% to be useful.

Replacement costs are falling. In 2020, a battery pack replacement could cost $15,000. Today, it’s closer to $7,000-$10,000 for most models. And third-party rebuilds are popping up-companies that take old packs, replace dead cells, and sell them for 40% less than OEM.

Some EVs, like the Chevrolet Bolt, had early battery issues. But most modern EVs are built to last. The Nissan Leaf from 2013? Many still have over 80% capacity today. The Tesla Model S from 2015? Still hitting 90%+ in well-maintained examples.

How to Maximize Your EV Battery Life

You can’t stop degradation-but you can slow it down. Here’s what works:

• Charge to 80% for daily use-Only go to 100% when you need the full range for a trip.
• Avoid fast charging daily-Use Level 2 (240V) chargers at home or work. Save DC fast charging for road trips.
• Don’t let the battery sit at 0% or 100%-If you’re storing your EV for a week, keep it at 50%.
• Use preconditioning-Heat or cool the cabin while plugged in, so the battery doesn’t have to work hard during driving.
• Keep it cool-Park in the shade or garage. Heat is the enemy of lithium-ion batteries.

These aren’t just tips. They’re based on real data from fleet operators, universities, and battery labs. The people who get the most miles out of their EVs aren’t the ones who charge to 100% every night. They’re the ones who treat the battery like a tool, not a toy.

Is Battery Degradation a Dealbreaker?

No. Not if you know what you’re getting into.

EVs aren’t perfect. But they’re getting better every year. The average EV owner drives 12,000 miles a year. Even with 2% annual degradation, a 250-mile EV will still have over 200 miles of range after 10 years. That’s enough for 95% of daily trips in the U.S.

And if you’re worried about resale value? A well-maintained EV with 85%+ battery health holds its value better than most gas cars. Buyers are learning to check SOH before buying used EVs. They’re not scared of degradation-they’re just checking the facts.

The real risk isn’t the battery dying. It’s assuming it will last forever without care. Treat your EV battery like a smartphone: don’t overcharge it, don’t let it get too hot, and don’t run it down to zero every day. Do that, and you’ll get 10-15 years out of it. That’s longer than most gas cars last.