EV Battery Degradation Calculator

What 22,700 real EVs say about degradation

Battery degradation is one of the few EV questions where the anecdotes and the data point in opposite directions. The largest published dataset — Geotab's April 2026 analysis of more than 22,700 vehicles across 21 makes and models — puts average capacity loss at 2.3% per year, which projects to about 81.6% of original capacity at eight years. That is worse than their 2024 figure of 1.8%, and they attribute the change to how EVs are now being charged rather than to the batteries themselves.

The average is the least interesting number in the study. Split by charging behavior, the fleet separates cleanly:

• Fast-charging in under 12% of sessions: 1.5% a year, projecting to 88% capacity at eight years.
• Fast-charging often, but mostly under 100 kW: 2.2% a year.
• More than 40% of sessions above 100 kW: 3.0% a year, projecting to 76% at eight years.

Climate adds another 0.4 percentage points a year for cars living in hot conditions. Those four numbers, plus the shape of the curve, are what the calculator above is built on.

The curve is steep, then flat — which is why year one scares people

Lithium-ion packs do not lose capacity at a constant rate. The first year or two takes a disproportionate bite, then the rate levels off into a long, slow, nearly linear decline. The mechanism is well understood: a passivating film grows on the anode the moment the cell is first charged, and it consumes lithium as it forms. Film growth is diffusion-limited, so it slows down as the film thickens — fast at first, then a crawl.

The practical consequence is that owners misread their own data constantly. A new EV that shows 3% loss after twelve months is not losing 3% a year; it has just finished the expensive part. Extrapolating that first year linearly predicts a dead battery around year twelve, and it is the single most common way people talk themselves out of an EV. The calculator handles this by aging the calendar term as the square root of time, so early loss is front-loaded and the tail flattens the way the fleet data does.

Mileage, by contrast, does behave roughly linearly. Cycle aging tracks energy pushed through the pack, so it scales with the odometer rather than the calendar. The calculator converts your miles into equivalent full cycles — odometer divided by rated range — which is why a 400-mile Lucid and a 250-mile crossover with the same odometer come out differently.

Does DC fast charging actually matter?

Here the evidence genuinely conflicts, and it is worth understanding why before you rearrange your life around it. Geotab's fleet numbers say heavy high-power fast charging roughly doubles the annual rate. Recurrent compared 13,000 Teslas that fast-charged more than 70% of the time against those that did it under 30% of the time and found no statistically significant difference in range degradation.

Both can be true. Geotab's heavy fast-chargers are commercial vehicles that also drive far more miles, so charging habit and cycle count are tangled together in a way the study cannot fully separate. Recurrent's fleet is Teslas — liquid-cooled, aggressively managed, and pre-conditioned before a Supercharger stop. The honest synthesis is that on a modern, actively cooled pack, routine fast charging costs you something measured in single percentage points over the life of the car, not tens. That is the size of the effect this calculator models, and it is why the DC fast-charge slider moves the answer less than internet folklore suggests.

What is not in dispute: fast-charging a hot pack, or repeatedly pushing past 80% on a fast charger where the taper makes it slow anyway, is where the real stress concentrates. Precondition before you plug in, and stop at 80% unless you actually need the miles.

How to slow battery degradation

Ranked by how much the evidence supports them, not by how often they get repeated:

1. Park in the shade, and out of the heat. Heat is the largest controllable factor in the fleet data — larger than charging habits. A garage, a carport, or a covered spot at work does more for a pack over a decade than any charging discipline. Ambient temperature ages the battery whether the car is moving or not.
2. Keep the daily charge ceiling at 80–90%, if you have a nickel-based pack. Time spent at a high state of charge accelerates aging. If your car has an LFP pack, do the opposite and charge to 100% regularly — the battery management system needs the full charge to calibrate. Your owner's manual says which chemistry you have.
3. Do most of your charging on Level 2 at home. The effect is smaller than you have been told, but it is not zero, and home charging is cheaper anyway. If you are weighing the install, the home charger ROI calculator prices it out — battery longevity is a bonus, not the reason.
4. Precondition before fast charging. A cold pack accepts a fast charge badly and a hot one accepts it destructively. Navigating to a fast charger in-car triggers preconditioning on most modern EVs, and it is the single most useful button you are probably not pressing.
5. Avoid leaving the car at 100% or near 0% for days. Storage at either extreme is harder on cells than driving through the same range. Before a long trip away from the car, leave it somewhere near half charge.
6. Stop worrying about the rest. Hard acceleration, regenerative braking, and the occasional 100% charge before a road trip are not meaningfully aging your pack. The battery management system is doing more to protect the cells than you can.

What your warranty actually promises

Federal law requires an EV battery warranty of at least eight years or 100,000 miles. Most manufacturers pair that term with a capacity floor — commonly 70% of original capacity — below which they will repair or replace the pack. Read the specific language: the term and the capacity threshold are separate promises, and a few brands warrant the term without committing to a number.

California wrote stricter durability rules into its Advanced Clean Cars II regulation for 2026-and-later models, requiring 70% of range be retained out to 10 years or 150,000 miles. Congress disapproved the federal waiver those rules depend on in June 2025 and the matter is in litigation, so treat California-specific coverage as unsettled rather than guaranteed, and check the warranty booklet for the car in front of you.

In practice the warranty is a backstop that almost nobody uses for gradual wear. Across all model years, Recurrent finds fewer than 4% of EVs have had a battery replaced; among 2022-and-newer vehicles it is roughly 0.3%. The replacements that do happen are overwhelmingly manufacturing defects surfacing early, not packs that slowly wore out.

Estimates only. Degradation rates and the shape of the aging curve are calibrated on Geotab's 2026 battery health study (22,700+ vehicles, 21 makes and models, published April 2026) and Recurrent's fast-charging analysis (13,000 Teslas). Battery capacity and EPA range figures come from fueleconomy.gov and manufacturer specifications, 2025–2026 model years. California durability rules: CARB Advanced Clean Cars II. Battery data changes as fleets age — verify against the current study year before relying on these figures.