Whilst sat on your driveway, most cars will have their alarm and immobiliser switched on protecting the car – however, these protection devices will also be slowly draining the vehicle battery.
How long your vehicle's battery maintains enough charge to start will depend upon the age and type of battery, the level of electronic enablement on your vehicle, engine size, and whether your vehicle is well maintained ensuring it typically starts instantly. Battery charge could range from a couple of weeks up to 2-3 months.
Obviously, batteries need charging otherwise they go flat. Your vehicle is fitted with an “alternator” which, when the engine is running, charges your vehicle battery. It usually takes around 20 minutes for the alternator to replace the energy used to start your vehicle, so if you only do ad-hoc short trips (e.g. to the local station, supermarket or school), your battery may never really be getting the full charge it needs. Combine this with an extended period of inactivity and you can expect a flat battery.
If you have an electric car, it’s best to give it a full charge and keep it plugged in if you can. Its on-board electronics will ensure it stays topped up and it won’t be drawing charge all the time.
Run your engine regularly. Letting your engine run for 15-20 minutes once a week will allow the alternator on your car to charge the battery. Make sure to do this outside or leave the garage door wide open for ventilation.
A jump-start might not always be the best option. Modern cars have increasingly complex electrical systems which could potentially get damaged by a sudden power surge if you use jump-start leads (i.e. attaching leads to another car to start your engine). If you are unsure, always check your car owner’s manual or, if in doubt, contact your car manufacturer or their local dealership for advice.
Consider purchasing a battery charger. A trickle charger can be connected to your car when not in use and will help keep the battery in peak condition. Use this in conjunction with a plug timer and you have a perfect set up. Two hours on trickle charge every day will help keep things stable, active and reliable.
Alternatively, a standard battery charger can be connected every couple of weeks for a few hours to return your battery to full charge. Ensure you purchase and connect the right charger to your vehicle so to avoid damaging your battery or shortening its lifespan (e.g. a modern hybrid engine battery typically needs a more sophisticated charger).
Ultimately, if you have a flat battery and are unsure what to do, contact a breakdown service who will be able to help you.
NOTE: If you are an NHS worker, the AA is providing free breakdown service to and from work during the coronavirus crisis whether you’re an AA member or not. Call the AA, 24/7, on your dedicated NHS number 0800 072 5064 or for more info visit https://www.theaa.com/breakdown-cover/nhs-covid-19-service