How long will electric vehicle batteries last? Tesla’s Roadster could be a guide
The question of battery longevity does not have a simple solution. Many factors affect cycle life of a battery pack, most notably climate, charging habits, driving style, and battery chemistry, and all the tests in the world cannot exactly replicate how each individual driver will use the battery over the life of the vehicle. How long will your vehicle’s battery hold on before being reassigned to a solar system on someone’s roof?
One of the most important variables in battery longevity is temperature. In general, temperatures above 86 degrees F place great stress on the battery and speed up capacity loss. Vehicles that have a liquid-cooled battery, like the Chevrolet Volt or Tesla Model S, are less vulnerable to high-temperature effects as long as they are not parked in the blazing sun.
However, the Nissan LEAF may be notably susceptible to rapid degradation in extremely hot climates. The results of an Idaho National Laboratory study released in March found that the test LEAFs lost 22-26% of their initial capacity after just 40,000 miles. This is most attributable to two factors: the vehicles were tested in Pheonix, where the hot climate accelerated capacity decline; and the vehicles were discharged to less than 5% capacity twice per day.
The second of those factors should not be overlooked. Charging habits, or depth of discharge, directly affect how long the battery will last. It is a well-established fact (though not widely known among the general public) that lower depth of discharge leads to longer cycle life. This is the reason conventional hybrid vehicle batteries can last for the life of the vehicle despite undergoing tens of thousands of charge and discharge cycles in routine driving over their lifetime.
An electric vehicle battery does not last as many cycles because it is discharged much more with each cycle. While a conventional hybrid battery will maintain a low depth of discharge, perhaps 30% of the battery’s usable capacity and last tens of thousands of cycles, a plug-in electric vehicle battery will allow a much higher depth of discharge window (up to 70-80% of usable capacity) in order to achieve more range. The trade-off is that the battery will have a much shorter cycle life, on the order of hundreds of cycles for a lithium-ion battery depending on the depth of discharge and the particular battery in question.