A car that is not being driven is still using power. The alarm, the keyless entry receiver, the telematics unit and the control modules all draw a small current around the clock. Over a weekend that does not matter. Over three or four weeks of summer travel, in a hot car park, it can be enough to flatten the battery completely.
How long a battery lasts without driving depends on the car, the battery's condition and how much it draws while parked, so there is no single answer. A healthy battery in a car with a low parked draw may manage several weeks; an older battery in a car with lots of electronics or an added dashcam may not last a fortnight. The good news is that a little preparation before you fly makes a flat battery on your return far less likely.
What drains a battery while the car is parked
The small, constant current a car uses when it is switched off is called parasitic draw. Every modern car has some. It powers things that need to stay awake so the car works when you return:
- The alarm and immobiliser, which monitor the doors and sensors.
- Keyless entry, which listens for the key fob.
- Telematics and connected-car services, which may wake the car to check in.
- Clocks, radio presets and the memory in control modules.
- Added accessories, especially dashcams with a parking mode, trackers and aftermarket alarms.
What is a normal amount of drain?
Once a car has gone to sleep after being locked, its parked draw is typically in the range of tens of milliamps. The acceptable figure differs from car to car, so check the manufacturer's figure in the handbook or service information, or ask the technician. Some cars take a while after locking before the modules go to sleep, so a reading taken straight away can look high.
A draw well above the normal figure usually means something is staying awake: a faulty module, a light that stays on in the boot or glovebox, or an accessory wired straight to the battery. A parasitic drain test finds this. If your battery goes flat after only a few days parked, that is worth checking before any long trip.
Heat adds to the problem. Batteries self-discharge faster when they are hot, so a car parked through July loses charge more quickly than the same car in winter.
Your options before you travel
There are four common approaches. None suits every car or every building, so pick the one that fits your situation.
| Option | How it helps | Things to consider |
|---|---|---|
| Disconnect the negative terminal | Stops all parasitic drain, so the battery only loses charge through self-discharge | The alarm will not work, and the clock, radio presets, window positions and some settings may reset. On some European and premium cars this can trigger warning messages, so check the handbook first |
| Use a battery maintainer | Keeps the battery topped up with a small, controlled charge | Needs a power point near the bay. Many buildings have rules on chargers and cables in car parks, so check with your building management first |
| Ask someone to start and drive the car | Recharges the battery and keeps the car moving | A short idle in the car park is not enough; the car needs a proper drive of around 20 to 30 minutes. The person will need the key and permission to use your bay |
| Book a battery test before leaving | Tells you whether the battery is healthy enough to sit for weeks | A weak battery is far more likely to go flat, so replacing it before you leave can save a call-out later |
Pre-travel checklist
Run through this list a few days before you fly, so there is time to sort anything that needs fixing.
| Check | Why it matters |
|---|---|
| Test the battery and charging system | A weak battery is the main reason cars do not start after a long park |
| Drive the car for a longer run the day before | Leaves the battery as fully charged as possible |
| Switch off or unplug the dashcam parking mode | Dashcams are one of the biggest sources of extra drain |
| Check all lights, including boot and glovebox | A light left on can flatten a battery in days |
| Lock the car and keep the key away from it | A key left near the car can keep keyless systems awake |
| Decide on disconnecting, a maintainer or a driver | Pick the option that suits your car and your building |
| Arrange access for an authorised contact | Lets someone deal with a flat battery without you flying back |
| Note the car's location and your parking bay number | Makes it quicker for anyone to find the car |
Extra care for stop-start and AGM cars
Cars with stop-start usually have an EFB or AGM battery and a battery monitoring sensor that manages charging. These cars often have more electronics, so their parked draw can be higher, and they are more sensitive to a battery that has run low.
AGM batteries handle repeated cycling better than flooded ones, but running them completely flat still causes lasting damage, and they need the right charging profile. If you use a maintainer, choose one that has an AGM setting and set it correctly. On many European cars, disconnecting the battery can also reset settings or bring up warnings until the car relearns, so check the handbook before you remove a terminal.
If a stop-start car comes back with a flat battery, expect the stop-start function to stay off for a while after recharging. That is normal; the car is protecting the battery. If it stays off for days, have the battery tested.
What to do when you get back
If the car starts, drive it for a proper run of at least half an hour rather than a short trip, so the alternator can put charge back. A slow crank on the first start is a warning that the battery has been stressed, so book a test.
If the car does not start, a jump start will usually get it going. Our jump start visit is a flat AED 99. But a jump is a way of moving the car, not a cure. After a deep discharge, the alternator may not fully recharge the battery on a normal commute, and the battery may have lost capacity for good.
Repeated jump starts after deep discharges shorten battery life. Each time the battery is run completely flat, sulphate hardens on the plates and some capacity is lost permanently, and this happens faster in the heat. If the car has needed a jump after your last two trips, the battery is likely near the end of its life, and testing will confirm it.
When the technician comes out, the battery and charging system are tested before anything is replaced. If the battery is healthy and only flat, you will be told so. If it needs replacing, fitted batteries start from AED 249, and the old battery is taken away for recycling.
Questions
How long can a car battery last without driving?
It depends on the car's parked draw and the battery's condition. A healthy battery in a car with low draw can often sit for a few weeks; an older battery, a car with lots of electronics or an added dashcam may go flat much sooner. Heat shortens the time further.
Is it safe to disconnect my battery before travelling?
On many cars, yes, by removing the negative terminal. The alarm will not work, and some settings may reset. On some European and premium cars it can cause warning messages, so check the handbook first or ask a technician.
Can I leave a battery charger connected in my building's car park?
Rules vary between buildings. Some do not allow chargers or cables in parking areas, and many bays have no power point. Check with your building management before relying on a maintainer.
Is starting the car once a week enough?
Starting it and letting it idle for a few minutes often puts back little more than the start used. The car needs a proper drive of around 20 to 30 minutes to recharge the battery.
My car does not start after I got back. What should I do?
Book a jump start, then have the battery tested. A deep discharge can damage the battery even if it starts again, and a test shows whether it will cope with normal use.