Why is my car’s battery draining and ways to prevent it

There are many causes for battery drain. Your car’s battery could lose charge if the car is kept parked for too long. This is true for all cars, whether they are petrol, diesel, hybrid or electric.
Even when your car isn’t being used, many features are running in the background – the security alarm, on-board computers, the clock, power doors, power locks, and presets like seat positions, the radio and climate control settings. All these functions use power and so drain the battery over time. While the daily power loss is minimal, the amount of battery discharge can be significant if your car stays unused for a long time. Eventually, the battery will completely discharge if it’s left uncharged. Jump to: Eight reasons your car’s battery is draining quickly Ways to prevent your car’s battery from draining What can drain an electric car’s battery? Ways to keep your EV battery healthy

If your car battery is draining, there are several potential reasons.

A common reason your car is losing charge quickly is that you forgot to turn your car off properly. For example, you left the headlights or the interior light on, or the boot or your door isn’t shut all the way.
Some cars automatically shut the lights off if they’ve been on for too long or send a warning beep, but many cars still require manual effort. If your car’s not being fully turned off regularly, the battery’s lifespan might shorten due to the constant drain. Check doors and lights before you leave the car, to ensure everything is switched off and locked up properly.

A parasitic drain refers to when your car’s battery continues to drain even after the car’s parked, and the amount of drainage is much higher than normal.
Usually, it’s a faulty accessory in the car causing the drain – for example, a sensor or interior light doesn’t switch off automatically. The accessory will keep consuming power until it’s manually switched off. Other such faulty accessories can include a damaged relay switch, computer module, alarms, headlights, boot or glovebox lights, or other electrical components. If you think you have a parasitic drain, a mechanic can easily diagnose this by performing a parasitic current draw test.

An alternator recharges your car’s battery whenever it’s put in gear and provides a constant flow of power to your car’s accessories.
If the alternator diode becomes defective, you may hear unusual noises, notice flickering lights or experience other issues with your car. Once the alternator fails, the battery will keep draining and eventually fail when you try to start your car. In this scenario, you’ll have to jump start your car - this will help your car get enough power to drive down to a workshop.

Your car’s battery can start causing problems as you use your car over time. If your car’s battery is old and worn-out, you may notice corrosion or a drop in performance.
If you see these signs on your car’s battery, it may be that it’s time to get a new one. You can confirm this by getting the battery checked by a professional. If the battery keeps dying even after you jump start the car, it means that there’s no life left in it. While the average age of a battery is typically five years, its life depends on various factors such as how often it’s used, the weather conditions and how much strain is put on it.

The battery supplies a surge of power when a car starts. Once your car is on the road, the alternator recharges the battery to make up for the power used to start the car and keep it running.
So, when you take a short trip, the alternator may not get enough time to recharge the battery again. Thus, frequent short trips can damage your car’s battery.

Your car battery has positive and negative terminals, to which cables are attached. Before doing any maintenance work on your car it is standard practice to disconnect these for safety reasons.
Make sure you reconnect them correctly – most batteries have a plus and minus symbols to identify the terminals and the convention is usually a red cable (or connector) for positive and black for negative, though this may not always be the case. Always disconnect the negative cable first. If these cables become loose, the battery can discharge. Signs of loose cables include flickering headlights, problems starting the car and a hot ground wire cable. This can be fixed by tightening the cables and re-installing them properly, though you need to bear in mind safety considerations when working on car electrical systems to avoid shocks or damage to the vehicle, while hybrids or electric models should only be worked on by qualified mechanics. If you are in any doubt whatsoever get professional help. Corrosion around the battery terminals can be another reason for your battery’s poor performance. Taking the safety considerations above in mind and having disconnected the battery cleaning the terminals with a brush and diluted baking soda mixture and then applying petroleum jelly to them before reattaching the cables can help but, again, only do this if you are confident you know what you’re doing.

Extremely hot or cold temperature can affect your car’s battery’s performance. The temperature affects the chemical reactions taking place in the battery, which can affect the battery's efficiency and strength.
In winter your car can need twice as much power to start. In summer, your battery’s vital liquids can evaporate, which can lead to corrosion and higher chances of battery failure.

You should drive your car after every few days so that the alternator can do its job and keep your car’s battery from getting completely discharged. Driving regularly also keeps the engine lubricated and corrects flat spots by reducing the strain on the bottom of the tyres.

Frequent short trips can strain your car’s battery. To avoid that, you should use your car for a longer period of time once on the road.
You can also consider investing in an external battery charger to maintain the correct voltage if you can’t use your car often, and for long journeys.

Make sure you switch off your car properly – and this doesn’t just include locking the car.
Before getting out of your car, check that the interior and headlights are off and all accessories like the phone charger socket and USB ports are switched off. Using the radio or GPS once the engine is off will drain your car’s battery too, so make sure you turn them off.

You can inspect your car’s battery by lifting the bonnet and checking for signs of wear and tear yourself, or with the help of a professional.
While checking the battery, you should ensure: • The battery is fastened tightly • Top of the battery is clean and free from dust and grime • Battery terminals aren’t corroded • Voltmeter should be around 12.7 volts or above

Your car’s dashboard usually has a battery symbol that illuminates if the battery is down.
Other signs that your battery is draining quicker than it should are: • Your car starts making unusual noises • The dashboard lights become dimmer • The car accessories aren’t functioning effectively • You hear a click when you turn the ignition key • If you notice these signs, you should inspect your car immediately or get it checked by a professional before the battery deteriorates further

You should try and keep your car in a garage – this helps in protecting the battery from extreme weather.
If you don’t have a garage, park your car in the shade. You can also consider investing in a battery blanket to prevent car fluids from freezing in winters.

A trickle charger uses the battery regulator to charge your car’s battery with the same amount and speed as it discharges when your car’s not being used. This prevents the battery from overcharging or becoming flat if your car’s been parked for a long time. This is particularly helpful for a second or ‘weekend’ cars that you may keep parked up for long periods and only use for special occasions.

Electric cars can suffer battery drain because of extreme temperatures, damaged batteries and parasitic drain, just like conventional cars.
Another reason why your electric car’s battery might be draining is due to faulty charging. If your electric car’s battery isn’t charged, the problem could be a damaged charger. A common reason for the damage is if you run over untethered charger cables the connector plugs on the floor. Careless handling, overuse or dropping the charger can also be responsible for impairing your EV charger.

Constantly charging your EV to 100% can increase internal resistance and reduce the battery’s efficiency and life.
While most electric cars have built-in battery management and monitoring system that stops charging once the car is fully charged, it’s best to switch off and unplug the charger.

Just as overcharging your electric car’s battery can be damaging, so can letting it get to zero per cent.
The recommended amount of charge for electric cars is usually between 15-90% or sometimes 25-75%, depending on each manufacturer. This helps in avoiding straining your battery for a prolonged period of time and thus keeps your battery healthy. If your car comes with the option to pre-set a charging percentage, you should stick to the manufacturer’s recommended charge state.

Charging your EV at room temperature (around 21.5-23°C) can help in charging efficiently.
During winters, the battery chemicals react slower than usual which can impact and slow down performance. Charging in hot weather or right after your car has been driven reduces the longevity of the battery due to the prolonged exposure to heat. While the damage is small, it can be irreversible. Many EVs come with a built-in thermal management system to keep them cool in summer, however, it’s best to park in a garage or find a shady spot.

Repeated usage of a fast charger can lead to degradation of the battery, especially during winter.
When you charge a battery, it becomes hot because the charging process moves ions around the battery. Using a fast charger generates even more heat because more power is required, which leads to battery degradation.

Deactivating presets helps switch off any unnecessary accessories or features that might be running in the background and saves battery.
Most of the latest cars come with various features that are responsible for draining your car’s battery. Leaving them switched on when the car’s not in use can quicken battery drainage.

If you want more tips and advice on maintaining your car, head to our advice section.
You can also find more information about electric cars with our dedicated EV collection. Related: • Storing your car during lockdown • Electric car batteries explained • Electric car charging at home