Your EV's 12V Battery Explained: How to Keep It Healthy

Electric cars have two batteries — the big high-voltage pack that drives the car, and a smaller 12V battery that keeps the basics running. Here's what the 12V battery does and how to avoid a flat one.

Ask most people what powers an electric car, and they'll say "the battery". If you've been wondering why your car battery keeps going flat in an EV, or how to maintain a 12V battery, this guide explains the whole system. But your EV actually runs on two batteries working together. The high-voltage pack gets all the attention, yet it's the smaller 12V battery that quietly keeps your car usable every day. Understanding how it works — and what drains it — saves you a surprise flat battery down the track. It's the kind of knowledge that's only useful until you need it, and then it's essential.

Two batteries, two jobs

• The high-voltage battery is the heart of the car. It stores the energy that drives the vehicle. It also powers the air-conditioning, wireless charging and the 12V battery's own top-ups.

• The 12V battery is the supporting system — and understanding its role is the first step in EV battery maintenance. While the car is parked, it powers the sensors, door locks, security features and app-based remote controls. In short, it's what lets you unlock, secure and wake your car.

How long does the 12V battery last?

The 12V battery is a wear item, and its car battery life is generally at its best within the first three years or 60,000 kilometres. But in real-world use, several things can shorten its life:

• Frequent short trips, which don't give the system time to top the battery up properly.

• Checking the car on the app repeatedly while it's parked and sleeping.

• Extreme heat or cold, which accelerates wear.

• Driving on a very low high-voltage charge, or leaving the car idle for long periods in that state.

These habits slowly drain the 12V battery until it can't do its job — a classic case of a 12V battery dying quietly.

What happens when it runs flat

A flat 12V battery is more than inconvenient. The most common symptom is that the doors won't unlock — the car's electronics have no power to respond. Your mechanical key still works in the door lock, so you can always get in. Beyond that, the car's remote functions and security features stop working until the battery is charged or replaced. Beyond that, the car's remote functions and security features stop working until the battery is charged or replaced.

How to avoid a flat 12V battery

• Keep the high-voltage battery reasonably charged. Driving on a very low charge for extended periods stresses the whole system, including the 12V battery.

• Don't obsess over the app. Checking the car's status a few times a day is fine; constantly waking the car while it sleeps adds unnecessary load.

• Recharge promptly. If your high-voltage battery has been low for a while, plug the car in. The system tops everything up for you.

• Park with enough charge for long periods. This is one of the most important electric car battery tips for owners who park for extended periods. If the car will sit unused, keep the high-voltage battery between 30 and 60 per cent charge. The same guidance that protects the main battery also protects the 12V system.

Get it checked at service

When your car is serviced, the technicians check the 12V battery's health as part of the routine. If its health is low, or the car's monitoring system sends a warning, replace it promptly. A failing 12V battery can leave you locked out or stranded. If you're planning a long trip, have it checked beforehand.

The bottom line

The 12V battery is small, but it keeps your EV usable. Charge sensibly, avoid constant app-checking, park with the right state of charge and let the technicians check it at each service. Do that, and you'll never think about it again — which is exactly how it should be.