How long do electric car batteries last?

The lithium-ion battery gets bad press. When it's not catching fire in advanced new laptop computers, smartphones and airliners, it's giving up the ghost ahead of its time in older electric cars.

Sadly, the press in this instance isn't 'fake news'. Li-ion batteries certainly have caught fire – that's for sure – but of more importance to new-car buyers, as the battery ages, its storage capacity diminishes and the vehicle's range gradually declines with it.

Extreme temperatures (very cold or very hot) over a long period will almost certainly reduce the battery's energy storage capacity. Areas where it snows in winter or where bushfires blaze in summer are inimical for EVs. Thus, active thermal management in an electric car is absolutely essential.

The battery is often tucked away out of sight, in a small space with little airflow to keep the battery cool. It has to be that way, because every element of a car needs to be robust and resistant to adversity – a sudden downpour or a car crash, to use two examples.

But isolating the battery from weather and heavy impacts can lead to extreme heat building up in the battery and lessening its working life.

That's why more sophisticated EVs run elaborate cooling systems to maintain the battery at a moderate temperature. These cooling systems are frequently used in hybrid and plug-in applications as well – since most of those vehicles are also fitted with lithium-ion batteries.

The first generation of Nissan LEAF launched in Australia with a 24kWh battery, and employed 'passive' air cooling that relied on convection – the heating or cooling effect of air flow – to cool the battery.

As a general consensus, this 'passive thermal management' system is not an optimal solution for cooling EV batteries, and unsurprisingly, the LEAF has a reputation for rapidly diminishing battery charge in the first generation model.

Nissan claimed that the LEAF battery would retain 80 per cent of its charge up to five years, but owners in hotter climates have experienced around 20 per cent battery degradation after barely 12 months. US customers have been offered upgraded (30kWh) batteries with cells featuring heat-resistant 'lizard chemistry'. These batteries are fitted as standard to new cars built for the US from 2015.

International online publications specialising in electric cars are advising LEAF owners to arrange a replacement ('lizard') battery from Nissan if the car is still under warranty and the battery capacity gauge shows only nine of the 12 segment bars illuminating after a full charge.

In Australia the battery of the LEAF was covered for eight years right from the start.

For the Tesla Model S, a bespoke cooling system relies on the circulation of a 50 per cent glycol solution (mixed with water). It must work for Tesla and its customers, because European owners in a recent survey reported travelling distances of up to 350,000km without battery capacity falling below 90 per cent.

Some Model S owners have experienced battery capacity dropping below 85 per cent after less than 50,000km according to the survey, but the vast majority of Model S owners are not experiencing that sort of degradation.

BMW's i3 diverts airflow from its on-board climate control for passengers to keep the battery pack cool. Unlike the Tesla system, the i3's reportedly won't run if the vehicle is switched off and locked unless it's also plugged in at a mains power outlet. Although the i3 doesn't appear to have incurred the consumer backlash that the LEAF has, there are occasional reports of the i3 suffering premature battery degradation.

It's commonplace these days for car companies to sell their electric cars with an eight-year warranty for the battery. Hyundai says the battery of its Kona Electric will last well beyond that period, but doesn't stipulate whether battery degradation is covered by the warranty.

BMW claims that the i3's battery, with reasonable care and maintenance, should last 15 years, which the manufacturer advises is the nominal working life of the car.

So the answer – ideally – is your electric car's battery should last at least eight years, if you were to buy a new one today. A few years from now, battery life will hopefully improve on that.

You can improve on the eight years of battery life by some simple means. Fast charging is the latest buzz word in electric car punditry (it's actually two buzz words), but there's a school of thought that battery life will be enhanced if you recharge the battery at a slower pace.

So while it may take you 28 hours to recharge a Hyundai Kona Electric from the 10-Amp outlet in your garage, it's apparently better for the battery in the long run – and never mind your 'inconvenience'. The slower charging reduces the voltage load for the battery.

On that point, there's no need to recharge the battery fully anyway. Experts say that recharging to just 80 per cent of capacity will prolong battery life also. Similarly, owners should not regularly allow battery charge to fall much below 20 per cent without recharging. The same goes for your mobile phone, incidentally.

For a car like the Kona Electric, owners can probably 'top-up' the battery for a couple of hours each night and that will leave enough charge in the battery for a range of a couple of hundred kilometres the next day – without the battery charge falling below 20 per cent during the day.

Obviously there's some trial and error involved, but some modern EVs will actually allow you to set the recharge ceiling at 80 per cent of capacity, which makes life a bit easier.