Mobile phone batteries are rubbish after 2 years, and laptop batteries need changing every 4-5 years. So are electric car batteries any better? After all, the cost of replacing the battery in a Nissan Leaf can be $5,000 or more, and the cost of replacing a Tesla battery (outside of the 8 year battery warranty) is into the five figures. Hence we have written this guide to see whether you need to be concerned about the batteries of electric cars.

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The (simple) science

Lets start by talking about the science behind electric car batteries for a second. But don’t worry, we’ll be brief and not get too technical!

There are different types of electric vehicle batteries, although the most common form by now (and the one which is the standard nowadays) are lithium-ion batteries (LIBs) - the same as in mobile phones and laptops, albeit ones with much larger capacity (and cost!)

Used Tesla battery cells

LIBs are rechargeable and contain lithium based atoms with a non-zero electric charge (ions). A fully charged LIB will have ‘lots’ of negative ions stored, which ‘move’ to the positive electrode when they’re discharged (used). Then they move back when charged. In other words, a lithium-ion based battery simply involves atoms moving from ‘charged’ to ‘used’ positions within the battery. Unlike other forms of batteries, LIBs are quite efficient at being charged and discharged without becoming too inefficient too quickly.

A variation on LIBs are lithium-ion polymer batteries (LiPo) which are similar LIBs but which use a polymer based electrolyte (instead of a liquid based one). They’re more robust and flexible, and have a slightly lower chance of leaking electrolytes, but are more expensive and potentially have a lower capacity/range.

Battery capacity

LIB batteries in mobiles and laptops are advertised in mAh which measures electrical power over time. A Samsung Galaxy S8 has a 3000 mAh battery, for example.

However electric car batteries naturally need to be a lot bigger and the voltage they run at varies, so giving their capacity in mAh doesn’t make as much sense. Hence they’re advertised as kWh instead. For example, a Tesla Model S might have a 60 kWh LiPo battery.

If we really wanted to compare the two, though, we can convert the Wh to Ah by dividing by the voltage. A Tesla Model S runs at 375 volts, giving a 160,000 mAh figure from the 60 kWh battery: 53x times bigger than the mobile phone!

But mobile phones work (and are used) in completely different ways to electric cars, so this comparison is a bit pointless. After all, a mobile phone is on all day whilst a car is typically used for 30-120 minutes per day.

This is why electric cars tend to advertise their effective range instead. For example, the Hyundai Ioniq’s advertised range is 124 miles (200 kilometers). This allows potential buyers to make a much more informed decisions (on whether the car battery is good enough for them). After all, if your commute is 100 miles daily, it’s clear that the Ioniq’s range wouldn’t be sufficient for you because you would need to visit a charging station every day. Whereas if you’d only be doing 15 miles per day, it’d be fine for you as you would only need to charge once per week (maybe whilst doing the weekly shop?!)

But if someone told you the mAh is 100,000 or the LiPo is 28 kWh, you’d probably be (rightly) confused about what this means and walk away! So our advise, when considering electric car battery capacity, is to ignore everything but the effective range.

Average electric car battery lifetime

Depending on how you treat your battery (i.e. how you use your car, how you charge the battery - more below), car manufacturers are fairly confident that you should get good enough use for 7-8+ years.

After all, Nissan Leaf offer a battery warranty of 5 or 8 years (depending on the battery you buy), Tesla’s is also 8 years and the Chevrolet Volt has a 10 year warranty.

So you should be fairly safe when buying an electric car brand new, or even a well-treated used one which is only 2-3 years old. However you should start to be sceptical of used electric cars which are 5 or more years old: maybe they’re being sold because their battery’s range and capacity is reduced to a point where the car is too inconvenient.

The other caveat to mention is that the battery warranties naturally do not mean that your battery will be kept at 100% health. LIB/LiPo batteries do degrade (despite being better than older style batteries), and the warranties reflect this: they only cover you beyond a certain amount of capacity/cell loss.

Typical cost to repair or replace car battery

A Nissan Leaf battery replacement is around $5,000 in the US (£5,000 in the UK), whilst a Tesla battery replacement runs into the five figures. A Volt replacement is similar to the Leaf’s price, too: $4,500-$5,500.

Used Tesla battery cells

However Nissan have recently revealed a new scheme, to replace your battery with a refabricated one at a cost of around $2,850. This is a good solution for people whose Leaf’s batteries have lost 30-40%+ capacity but who don’t want to stump up $5,000 on a brand new battery.

Finally, you won’t always have to replace the battery. It might be that only certain battery cells have failed, and a repair for this could be as low as $500. But naturally, the cost will vary a lot depending on the exact issue and also the technology and expertise of the garage/dealer you go to.

Tips for preserving the battery life

Whilst there’s some debate, we’d agree that the ‘80-20’ rule is worth following for any lithium based battery: aka try not to charge it about 80% (as the battery heats up too much when charging over 80%), and don’t leave the capacity drop below 20% (as this stresses the battery).

This is because LIBs/LiPos have a certain number of full cycles available, before they become less and less efficient. Mobile phone batteries typically have 500-750 cycles, which is why people who charge their mobile to fully every night see their battery becoming rubbish after around 2 years (aka potentially 730 full cycles if the phone is discharged - ‘used’ - a lot throughout the day).

Some studies show that charging from 100% to 0% constantly leads to just 500 effective cycles, compared to 3,500 effective cycles when following the 80-20 rule: 7x more!

Having said all this, don’t worry if you do charge below 20% or above 80% from time to time.

In conclusion: are they good enough?

Short answer: yes!

Longer answer: see the article above, but still yes!

Massive gains have been made over the past decade with lithium-ion based battery lifespans, and even a well-used, 30%-degraded Nissan Leaf battery could yield a 117 mile (189 km) range. Plus the cost of repairing or replacing electric car batteries is dropping all the time.