Car Care: EV batteries and charging explained

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Every month, more and more electric vehicles (EVs) are being imported into New Zealand, but many of our motorists are still unfamiliar with the battery technology used to power them.

You can think of an EV battery as a new kind of fuel tank, as it effectively stores the fuel used to propel the vehicle. If you’re considering buying an EV, it’s important to understand the three main aspects of this “fuel tank” — capacity, charging and range.

Capacity: An EV’s battery is rated in kilowatt-hours or kilowatts per hour (kWh). This is a measurement of electricity for the amount of energy expended in 60 minutes by one kW of power. So the more kWh the battery capacity has, the longer the vehicle range. For example, a 2019 Nissan Leaf has 40kWh and an average range of 270km, whereas a 2018 Hyundai Kona EV has a range of around 400km thanks to its 64kWh battery. This shouldn’t be confused with the power rating of the actual electric motor which is measured in kilowatts (kW). The power of the motor is what produces the impressive torque.

Charging: There are currently three main methods for charging:

1. Home (via an In-Cable Control Box charging cable): This is designed to connect to a standard three-pin wall socket, but it’s a slow overnight charging method and will fully recharge a used Nissan Leaf in 6-8 hours or a Kona in around 43 hours.

2. Home (via a Fast Charge Wall Box): This is an optional wall box for your household and improves charge times by utilising a 16-32amp 3.7-22kW power supply. It can significantly reduce EV charging time at home but costs a few thousand dollars to purchase and install.

Public Rapid Charging Stations: This is the fastest way to charge an EV, and can take up to 75 minutes to charge a large capacity EV from 0 to 80 per cent, typically utilising 25-50kW DC charging.

Range: Battery range is dependent of environmental factors and load, so unlike petrol in your tank, you are draining the EV battery by having anything electrical on in the car. Thankfully, brake regeneration systems can put enough charge back into the battery to counter this and boost your range as you drive.

Two common terms you might hear when shopping for used EVs are “state of charge” and “state of health”. State of charge (SOC) is defined as the available capacity (in Ah) and expressed as a percentage of its rated capacity. State of health (SOH) represents a measure of the battery’s ability to store and deliver electrical energy, compared to a new battery.

As with a smartphone, over time an ageing EV battery can reduce in ability to store charge (SOH) while the demand from the motor’s power remain the same. This means that a full battery charge won’t last as long, resulting in reduced range.

The future: The next generation of EVs due to enter the New Zealand market over the next 12 months are meeting the demand for increased capacity DC fast charging systems in excess of 150kW, which can charge a high capacity EV like the new Audi E-Tron to 80 per cent in just 30 minutes.

It doesn’t stop there; the requirement for a quick high-capacity “dump” of electricity will also increase — it’s reported that the new Porsche Taycan will have the ability to accept an impressive 350kW.

EVs also have a battery warranty, typically 5-8 years or a set distance (ie 100,000km). It’s early days and we’re yet to see what an “expected” EV battery life looks like.

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