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What happens if your electric car battery goes flat?

What happens if your electric car battery goes flat?

The electric car revolution is upon us, but many buyers still have reservations about making the switch to electric drive. Contemporary electric cars have been on sale in their current form for around a decade since the Nissan Leaf first hit dealerships, and every EV for sale in Ireland is as straightforward to drive as an auto-equipped petrol or diesel car.

However, the distance that you can go in an EV is what worries a lot of people. While this so-called range anxiety is reduced every time a new model with a longer range is launched, some potential buyers still have concerns about being able to charge the battery, especially when out and about. And if you do run out of battery charge, then what happens?

Deep discharge

Read the owner's handbook of any electric car, and the section about the car's high-voltage battery will tell you that allowing the battery to go flat has the potential to damage the electric drive system. This is known as a deep discharge, and it can harm electrical components that could limit its charging capacity or its power delivery.

Most EVs will give you plenty of warning to recharge the battery well before you're running on empty, though. As a guide, getting the battery down to around 15-20% capacity will see the warnings start - much like a combustion engined car when you're down to the last couple of bars on the fuel gauge. Most EVs tend to have sat-nav fitted, and this will try and guide you to the nearest charge point to top up the battery.

Ignore these warnings, and the car will continue, but like a petrol or diesel car, the range read-out will finally go blank, confirming that the inevitable will happen. Some cars will go into a 'limp-home' mode that cuts power to the bare minimum – again much like a combustion-engined car - which gives enough energy to move the car off the road to safety, but not a lot else. It's worth noting that while an EV’s drive battery will be flat, the car's ancillaries (such as the hazard warning lights) should still work, because these run off the car's separate 12-volt battery.

Once the drive battery is flat, though, the vehicle will stop, and that's that.

Recovery mode

If the EV is in neutral, it should freewheel as easily as a combustion-engined car. That means it will be movable, although the heavy battery means you'll have to give it some effort to get it rolling.

Most new EVs will come with free breakdown cover for a situation as this, and the policy will include recovery to your home or the nearest EV charge point if the drive battery is flat. This is the best way to move an EV, since the car will either be carried on a flatbed lorry or with dolly wheels be placed under all four corners when being towed, to stop the EV's wheels from turning.

Once you're back at a charge point, it will be a case of waiting for the battery to be recharged, which highlights the other downside of running the battery flat - it'll take ages to charge up again. If anything, getting into this situation should get EV drivers into the habit of charging little and often to keep the battery at full capacity as much as possible.

Carzone - 09-Nov-2021