EV Battery Degradation Calculator

The Battery Degradation Calculator estimates remaining battery capacity based on vehicle age, mileage, climate, and charging habits using a research-backed model.

The Linear Degradation Myth

A persistent misconception holds that EV batteries lose capacity at a steady, fixed rate — say, 2–3% per year, every year, until the battery is useless. Under this assumption, a 10-year-old battery would retain only 70–80% of its original capacity. This linear model is intuitive but wrong, and it consistently overestimates long-term degradation.

Fleet telemetry data from Geotab's 2024 study of over 10,000 EVs across multiple makes, model years, and climates reveals that degradation follows a curve much closer to the square root of time. Capacity loss is steepest in the first 12–18 months, then progressively slows as the battery's chemistry stabilises. The table below summarises observed average capacity retention.

Vehicle Age	Average Capacity Loss	Remaining Capacity
Year 1	~2.3%	~97.7%
Year 3	~4.2%	~95.8%
Year 5	~5.5%	~94.5%
Year 8	~7.0%	~93.0%
Year 10	~8.0%	~92.0%

A well-maintained EV battery at 10 years typically retains over 90% of its original capacity. That first-year drop of around 2.3% is not a preview of annual losses to come — it reflects initial chemical stabilisation. By year five, the annual rate of loss has slowed to well under 1% per year for most vehicles. This decelerating curve is why used EVs with 50,000–80,000 miles often show surprisingly healthy battery readings, and why the EV range estimator remains useful even for older vehicles with some capacity loss.

Calendar Aging vs Cycle Aging

Battery degradation occurs through two distinct mechanisms that operate simultaneously, and understanding the distinction helps explain why two identical vehicles can show different capacity readings.

Calendar aging is the slow chemical breakdown that occurs simply because time passes. Even an EV parked in a garage and never driven experiences calendar aging. The primary driver is a phenomenon called solid-electrolyte interphase (SEI) layer growth on the anode. This layer gradually thickens, consuming lithium ions and increasing internal resistance. Calendar aging is accelerated by heat and by high states of charge — a battery stored at 100% SoC in a hot garage degrades faster than one stored at 50% SoC in a cool climate, even if neither vehicle moves.

Cycle aging is the degradation caused by charging and discharging the battery. Every charge cycle causes microscopic structural changes in the electrode materials. Deeper cycles (discharging from 100% to near 0%) cause more stress than shallow cycles. High charge rates generate heat within the cells, which compounds the damage. Cycle aging is proportional to energy throughput — a vehicle driven 20,000 miles per year accumulates cycle aging roughly twice as fast as one driven 10,000 miles per year.

For most EV owners, calendar aging is the dominant factor in the first five years, particularly if annual mileage is below 12,000 miles. High-mileage drivers see a larger contribution from cycle aging. The calculator models both mechanisms independently and combines them for the total estimate. Owners interested in how degradation affects long-term financial outcomes can explore the total cost of ownership calculator, which factors in battery capacity decline.

Heat Is the Battery's Worst Enemy

Of all the variables that influence degradation rate, sustained high ambient temperature has the largest effect. Geotab's fleet data and NREL research both confirm that EVs operated predominantly in hot climates show approximately 30% more cumulative degradation at any given age than identical models in temperate climates.

The mechanism is straightforward: heat accelerates the chemical side reactions that cause both SEI layer growth and electrolyte decomposition. The relationship is exponential — the difference between 75°F and 95°F average temperature matters more than the difference between 55°F and 75°F.

Vehicles with active liquid cooling — including Tesla, Hyundai, Kia, and most newer EVs — maintain battery temperature within a narrow band during both charging and driving. The Nissan Leaf, notably, uses passive air cooling, which leaves its cells more exposed to ambient conditions. Leaf owners in Phoenix have reported 15–20% capacity loss within five years, while Leaf owners in Seattle with the same mileage typically see 5–8% loss.

Cold weather, by contrast, causes temporary range reduction but contributes relatively little to permanent degradation. The winter range calculator models the temporary cold-weather effect separately from permanent degradation.

DC Fast Charging: Less Scary Than You Think

One of the most persistent concerns among prospective EV buyers is that DC fast charging damages the battery. The data shows the impact depends entirely on how often you DC fast charge.

Studies from NREL and Idaho National Laboratory, along with Geotab's fleet analysis, consistently show that occasional DC fast charging — once or twice per week — has negligible measurable impact on degradation compared to exclusive Level 2 home charging. The additional degradation from regular but not exclusive DCFC use over five years amounts to approximately 1–2% of total capacity.

Exclusive DC fast charging over extended periods does show a measurable effect. Vehicles that rely on DCFC for the majority of their charging over five or more years show approximately 1–3% additional capacity loss. For most owners, this represents a minor trade-off against the convenience of fast charging during travel.

The reason DCFC is less damaging than feared is that modern BMS systems actively protect the cells. When a vehicle's BMS detects that cells are approaching thermal or voltage limits, it reduces the charge rate. Understanding the charging curve and session timing shows how this protection works in practice.

The factors listed below do have meaningful effects on long-term battery health.

• Sustained high ambient temperature (living in a hot climate year-round)
• Routinely charging to 100% and leaving the vehicle at full charge for extended periods
• Routinely depleting the battery below 10% SoC
• Very high annual mileage (above 25,000 miles per year)
• Passive (air-cooled) thermal management combined with hot climate

Controllable habits — charging to 80% for daily use, avoiding prolonged storage at 100%, and maintaining recommended tyre pressure — contribute to battery longevity. The charging schedule optimiser helps set up daily charging to 80% automatically.

Worked Example: Three-Year-Old Tesla Model 3

A Tesla Model 3 Long Range owner in Portland, Oregon, has driven 36,000 miles over three years. The vehicle charges overnight on Level 2 to 80% daily, with DC fast charging used roughly once a month. Portland's climate is mild (average annual temperature around 53°F).

Calendar aging at 3 years in a mild climate (factor 1.0): 2.3% × √3 = 3.98%. Cycle aging: 36,000 miles ÷ (341 × 0.6 miles per cycle) = 176 equivalent cycles × 0.015% = 2.64%. DCFC penalty: negligible. Total degradation: approximately 6.6%. Remaining capacity: 93.4%. On the 75 kWh pack, that translates to 70.1 kWh remaining. Estimated range: 341 × 0.934 = 318 miles.

This vehicle's battery is well within the healthy range at this age. The mild climate and Level 2 charging represent near-ideal conditions. The rate of loss will continue to slow — years four and five will likely add less than 1% combined additional loss.

Worked Example: Five-Year-Old Nissan Leaf in Arizona

A Nissan Leaf SV Plus owner in Tucson has driven 50,000 miles over five years. Charging is mixed (70% home Level 2, 30% public). Tucson's average annual temperature is approximately 70°F, with summer highs routinely exceeding 110°F. The Leaf uses passive air cooling.

Calendar aging at 5 years with hot climate factor (1.3): 2.3% × √5 × 1.3 = 6.68%. Cycle aging: 50,000 ÷ (212 × 0.6) = 393 cycles × 0.015% = 5.9%. DCFC penalty (mixed): 0.5%. Total degradation: approximately 13.1%. Remaining: 86.9%. On the 59 kWh pack: 51.3 kWh remaining. Estimated range: 212 × 0.869 = 184 miles.

The combination of Arizona heat and passive air cooling drives this noticeably worse outcome. Even so, 87% retention at five years is well above the 70% warranty threshold. Owners in similar climates can model the financial implications using the break-even calculator.

Calendar Aging

Calendar aging is the gradual loss of battery capacity that occurs as a function of time, independent of usage. It is driven primarily by chemical changes at the electrode surfaces, particularly solid-electrolyte interphase layer growth. Calendar aging is accelerated by high storage temperature and high state of charge. Even an EV that sits unused for years will experience measurable calendar aging, though the rate is slow under cool, moderate-SoC conditions.

Cycle Aging

Cycle aging is capacity loss caused by repeated charging and discharging. Each cycle causes small structural changes in the cathode and anode materials. Deeper cycles cause more stress, and high charge rates generate more heat. Cycle aging is proportional to energy throughput — it is the dominant degradation mechanism for high-mileage commercial vehicles.

Capacity Fade

Capacity fade is the overarching term for any reduction in a battery's ability to store energy compared to its original rated capacity. It encompasses both calendar and cycle aging effects. Manufacturers typically warrant EV batteries against capacity fade below 70% within 8 years or 100,000 miles. Capacity fade is distinct from temporary range reductions caused by cold weather, which are reversible.

Battery degradation is one of the most misunderstood aspects of EV ownership. Modern EVs with liquid-cooled battery packs routinely demonstrate capacity retention above 90% at the decade mark. The calculator above helps set realistic expectations grounded in fleet-scale data rather than worst-case anecdotes or best-case manufacturer claims. The companion five biggest battery degradation fears debunked with fleet-scale data walks through warranty terms, replacement costs, and charging habits in more depth.