Battery Life in electric cars
An important question for owners of Electric cars, and particularly those buying older cars.
Lithium Ion Batteries can be charged and discharged thousands of times, but as they are cycled their chemistry changes very gradually, reducing the total capacity available. This is normal operation of a battery, a predictable aging process which is managed by the Battery Management System. As a result the range of electric cars will reduce very slightly with each year, or each 10,000 Miles or Kilometres driven. Mobile Phone batteries, and all consumer goods with rechargeable batteries are subject to the same process but Electric Car batteries are more predictable and have much greater life, as they use excellent control systems to protect the cells.
How is battery Health (or condition) measured?
New electric cars advertise their predicted range on a full charge when driven on a standard test course. When new it is assumed that the battery state of health or condition is 100%. When the battery has aged to the 90% point, perhaps 3-5 years, one would expect to get 90% of the range on that test course, ie 225 Miles range. This measure of the % of original battery capacity remaining, is a key characteristic of a used electric car in addition to its age, condition and miles or Km on the Milometer. The diagnostic systems of electric cars will retain and divulge this % of original capacity when connected to a diagnostic computer.
Worth asking for this information when buying, but many sellers will not have this information.
Why do some cars show lower % battery health than others
The normal aging of a Battery is influenced by many factors, but Joe reckons the important ones are:
How old is the battery?
How much power has the battery delivered - related to the miles/Km on the clock, how hard it has been driven and how heavily loaded has it been - was it always full of people and luggage?
Has it frequently been exposed to strong sun/high temperatures ~ 30C+ Unfortunately this is never a problem where Joe lives, and is a reason the UK and Ireland are ideal places to run Electric Cars!
How frequently has the car been 'Fast Charged' on a public charger? Slower charging (as on a home charger) is generally better for battery health. There could be a disadvantage of buying used cars that are fitted with optional high speed charging ports if these were used frequently.
Premature Battery Aging and Faults
This is rare but like any machine, there is the possibility of faults occurring which cause the car to show reduced battery health. A small number of battery cells may have failed or degraded. This is usually visible in the vehicle diagnostics and a dealer should be aware and addressing this prior to sale, or advising the buyer. Such abnormal battery aging should be covered by the vehicle warranty over its term.
Displayed Range and Battery State of Health
All Electric Cars display the remaining range available (in Miles or kM) and the battery state of charge (ie is it fully charged 100% or less that fully charged, for example 30%). If battery is at or close to 100% charged, the range displayed can be used as a guide to the Battery State of Health, and the range the car is capable of, however the range displayed depends upon how economically the car has been driven recently. Wise sellers will demonstrate the car after economical driving - perhaps unrealistically so, hence a State of Health from the car diagnostics will be more reliable than estimates made from the range shown on the dash display.
Final Note - while Joe has never heard of a reported case, it is theoretically possible to falsify the battery state of health shown by a car, in the same way as Milometers were wound back in the old day!
the state of health of the batteries in used cars
Great Article from the Times
The article below published by the London Times newspaper is excellent on factors that impact life of Electric Car batteries, and includes a link to some data on how batteries are lasting on most common Electric Car models, from a large fleet of electric cars. Unfortunately Renault Zoe is not included in the data.
As well as allowing a comparison of average battery performance on most common models the data can show the average State of Health of cars of different ages. Batteries are lasting well.
The data presented is from Canadian Company Geotab. Good illustration of overall performance, but be aware that some individual batteries will have performed worse than shown here. You will need to enter data into two fields in the database (Make and Year) to access the data.