Electric car batteries explained

With an electric vehicle (EV), it’s all about the battery.

A battery pack is currently the most expensive component of an EV, but battery prices will lower over the next few years, as packs are built in higher volumes to meet demand for new EVs and can take advantage of economies of scale. Further on in the decade, we might also see new, less expensive types of battery.

Whatever its cost, the battery will remain one of the most important parts of any EV, as it determines how far a car will go when fully charged, how long it takes to recharge, how long it will last and almost any other aspect of the vehicle.

What is an electric car battery?

We’re not going to lie: making the most of a battery’s energy is still something of a dark art, with a load of physics and chemistry involved.

Yeah, us neither, so the good news is that a battery pack is all sealed up and only accessible to trained technicians. It should be reliable for a good few years, so we don’t have to worry too much about how it works.

That said, it’s always good to know the basics so, as the ads say, here’s the science part.

A battery pack is made up of lots of cells, which are packed together in modules. The modules are then packed together in a case, with all the electronics that enable the car to access the battery’s power. This is the battery pack.

Your EV battery is pretty much the same as the one in your smartphone or laptop. A lot bigger, obviously, but it’s a lithium-ion battery. This type of battery has the best energy density, which means there’s more available energy per cell than other types of battery.

There are currently lots of experiments with other ‘battery chemistries’, as they’re known, which means that we could see different types of batteries (iron phosphate, for example) in EVs in the coming years.

But for now, lithium-ion batteries are the only game in town.

How electric car battery energy works

The next thing to understand about batteries is their energy capacity, which is expressed in kilowatt hours (kWh).

For example, the Tesla Model S 75D has a 75kWh battery, while the Honda e has a 35kWh battery. The Tesla has a real-world range in excess of 200 miles, while the Honda’s range is just over 100 miles, largely because the Tesla’s battery is over twice the size of the Honda’s. In short, the bigger the battery in kWh, the more energy it can make available to the car.

However, when comparing EVs and their relative battery sizes, it’s worth remembering that cars such as the Tesla have higher-performance motors that produce more power and help it to a 0-60 time that is less than half of the Honda’s. If you decide to use that power when driving, your battery will empty quicker, so you won’t get the range you expect.

And if you consider that an EV uses an average of 2,000kWh of energy a year, that means you’ll have to charge a smaller battery – like the Honda’s 35kWh one – twice as many times as the Tesla’s.

Charging an electric car battery

Obviously, once your car’s battery is out of energy, it needs to be recharged.

You’ve probably noticed that EV manufacturers often quote the time it takes to achieve an 80% charge, not 100%. The main reason for this is that the last 20% takes longer to charge relative to the first 80%. However, if you want to look after your EV’s battery, you can extend its life by not charging it fully.

How quickly your EV charges depends on the type of charger you use, with different units having different charging speeds. Charging from a domestic three-pin plug is the slowest way, but if you can charge overnight, that will work for most owners. Then you have 7kW and 22kW chargers, which are either home-charging wall box units or the types of public chargers you find in car parks, on the street or at leisure centres or shopping malls. You can usually get to 80% charge in three or four hours.

Next fastest are the 43kW-50kW ‘rapid’ chargers, which you’ll find on motorway service stations, for example. In lust over half an hour, you can get an 80% charge.

The big breakthrough in recent years has been the emergence of 100kW, 150kW and even 350kW chargers. An 80% charge takes just 10-15 minutes.

Not all EVs charge equally fast, though. Some older EVs can only charge at 3kW or 7kW, so even if you plug them into a new ultra-rapid charger, they will only charge at the rate of 3kW or 7kW. More recent models – especially at the more premium and luxury end of the scale – can take electricity onboard at the rate the ultra-rapid chargers can pump it out.

Temperature is another factor in determining charging speed. Batteries operate optimally at between 20-25°C. If the outside temperature gets too cold or too hot, the EV’s battery management system (BMS) will reduce the power input to protect the battery. This reduction means that the car talks longer to charge.

Some of the latest, more performance-oriented EVs come fitted with a system that regulate the battery’s temperature, so it’s always at the right temperature when you plug in.

Electric car battery life

As EVs are still faily new, relatively speaking, it’s difficult to say how long a battery will last. There are lots of variables that govern a battery’s useful life, but early evidence suggests that the eight-year battery warranties issued by manufacturers are about right.

After 8-10 years, the batteries will still work, but they'll find it more difficult to hold a full charge. The good news is that there’s probably going to be a healthy market for second-use batteries.