Look After Your Car Battery
Without being used regularly, car batteries can lose charge meaning they may not have enough power to start the engine – this is likely to be the case if your essential journeys are especially short.
This is also more likely to be the case with cars with older, weaker batteries, but even newer or brand-new batteries can fail if they haven’t been used for long periods.
Why might my battery not start my car?
The optimum voltage for a car battery is around 12.6 volts – that’s the sign of a fully-charged battery. Yet strangely, a voltage of 11.9 volts indicates a battery is completely depleted and probably doesn’t have the power to start a car.
If a battery – new or old – falls below 11 volts as a result of not being driven or independently charged for a long period it starts to suffer internal damage, meaning it may not be possible to bring it back to life.
Of course, you’re unlikely to know the exact charge in your car’s battery, but there’s likely to be three main reasons why your battery isn’t starting your car:
The battery might be old and no longer holding its charge that well
The car has only been used occasionally for very short runs – as has probably been the case for many people during lockdown – so the battery hasn’t had a chance to charge
The battery has been drained – this could happen because accessories like dash cams have been left plugged in, or perhaps while washing your car you’ve had the radio and interior lights on. While even immobilisers draw some charge from a battery, the important thing to remember here is that any extra drain reduces the chances of your battery starting your car when you need it to, so always disconnect everything you can if it’s not going to be driven for a long period. For the time being, it might be best to unplug your accessories.
Using a trickle charger or battery conditioner
To reduce the chances of your battery failing you, especially if you don’t drive very often in normal conditions, you should consider using a ‘trickle’ charger or battery conditioner.
This is the most effective way keep your battery healthy for long periods with little or no use. It will also keep immobilisers and other energy-sapping components from draining your battery completely.
Just keep in mind that using these devices could be impractical if your car is parked on the street as you may need to drape cables across the pavement, which can become a tripping hazard for passers-by.
When charging your battery always refer to your manufacturer’s handbook and follow the instructions provided with the charger.
Just starting your car may do more harm than good
If you can’t use a trickle charger the best advice is to rely on your essential journeys to keep your battery healthy.
Simply starting a car occasionally and leaving it running for only a few minutes isn’t likely to help, in fact this may end up draining a weak battery, driving the vehicle for 15-20 minutes would, in most cases, be sufficient to top up the battery charge.
If there are two cars in your household you may want to consider alternating your essential trips in them. You should also be mindful that repeated short journeys will flatten your battery faster than usual, which is even more reason to follow the government’s guidance to shop for necessities as infrequently as possible1.
Electric vehicles and plug-in hybrids
EVs and PHEVs still rely on a 12-volt auxiliary battery to power systems which means they can go flat just like a conventional car when unused for a period of time.
The best way of maintaining the health of an EV’s 12v battery will vary from manufacturer to manufacturer, but may include putting the vehicle in ‘ready mode’ for a certain period of time every few weeks to recharge it. Check your vehicle’s manual to find out what’s recommended.
The main high voltage battery should not be left on charge permanently. It is generally recommended these should be maintained at around 50% charge but not allowed to drop below 30% if the vehicle is not in regular use.
Do I need a new battery?
If your battery’s reached the end of its life and you need to buy a new one, always make sure you choose one that meets or exceeds the specification for your vehicle.
One of the tests carried out by manufacturers is to ensure batteries have enough storage capacity to be able to start a car which hasn’t been used for a number of weeks.
But it’s important to note this test doesn’t take account of extra plugged in devices, like a dash cam, that might drain a battery and affect its ability to start a car.
Even brand-new batteries can have difficulty starting a car if they’ve not been charged up and discharged several times.
This is because most new batteries don’t leave the factory fully charged – they only reach their full charging potential by being driven regularly which is, of course, not the case during the coronavirus pandemic.
My battery is flat and my car won’t start. What can I do?
If you have another car with a charged battery parked close by the one with the failed battery, jump-starting is an option for you: