EV Battery Degradation Calculator

EV batteries lose capacity with age and with use, and the two do not add up. A car that sits in a driveway for eight years and one that covers 300,000 km in the same period both lose capacity, but for different reasons, so this calculator works out each figure and reports whichever is worse. Most warranties promise at least 70% capacity at 8 years or 160,000 km, whichever comes first.

The two rates:

Calendar loss = the annual rate for your charging habits × years

Cycle loss = 10% per 150,000 km driven

Result = the worse of the two

Annual calendar rates used here:

• Good habits (charge to 80%, home AC charging): 1.5% a year
• Average habits (occasional 100% charges): 2.0% a year
• Heavy use (daily DC rapid charging, regularly to 100%): 3.0% a year

Large fleet telematics studies put the real-world average near 2% a year, and newer model years do noticeably better than the 2013 to 2016 generation. Tesla reports its own fleet in miles rather than kilometres, with roughly 12% capacity loss at 200,000 miles, so a Tesla is likely to sit at the optimistic end of the range above.

Worked example:

A 75 kWh battery, five years old, 15,000 km a year, good charging habits.

• Calendar: 1.5% × 5 = 7.5% lost
• Cycle: 75,000 km × 10% / 150,000 = 5.0% lost
• Calendar is worse, so 7.5% applies: 75 × 0.925 = 69.4 kWh
• On a car rated 450 km when new, that is about 416 km

Drive 40,000 km a year instead and the cycle figure becomes 13.3%, which overtakes calendar loss and becomes the number that counts. Both figures are capped at 30%, because degradation flattens out rather than continuing in a straight line.

What actually accelerates it:

• Frequent DC rapid charging, especially pushing past 80%
• Sitting at 100% or near 0% for long stretches
• Heat above about 40°C without active thermal management

What slows it down:

• A daily ceiling of 80 to 90% instead of 100%
• Keeping the pack roughly between 20% and 80%
• Pre-conditioning before charging in cold weather
• A 7 kW home wallbox for daily charging, saving DC rapid for trips

The single biggest lever is the daily charge ceiling. Everything else on those lists is worth less than moving from 100% to 80%.