I remembered reading somewhere that we shouldn't start our cars with devices (GPS, cell phone, video game device, etc.) plugged into the cigarette lighter port. This is because when we start our car, there will be a surge of power going into our devices and messing up either it or the battery it's charging.

I don't know where I saw this before but I'm wondering is this true? Should I unplug all devices before starting or is this some sort of old wives tale? If this IS true, is there an article proving electrically/mathematically why it's bad?

  • 3
    I would say it's BS. The starter is a heavy load, and will cause the voltage throughout the system to drop, not spike. For proof of this turn on you headlights one night and then start the car.
    – Jrican
    Commented Oct 16, 2015 at 4:11

4 Answers 4


I'd say it's quite safe. When you start your car, there is a huge drop in battery power, not surge (remember how your lights dim the moment you start). Now, the undervoltage is not good for electronics either, but typical gadgets have 5V input and use an adapter (a buck converter actually) to transform 12V to 5V. Such converters are usually rated for a wide input voltage range (something up to 15V) and require about 2V for themselves to work correctly, so as long as the battery voltage doesn't drop below 7V or so, your gadgets don't even see any change on their power line.

For a second line of defence, most gadgets have an internal battery to fall back on, should the input voltage become unusable.

As a personal experience, I have been using a GPS plugged into my cigarette lighter for 3 years now. I also use a dashcam, which I unplug only when I need to charge the bluetooth handsfree or several of my mobile phones. None of these devices have had any power-related issues. If anything, I can suggest you don't unplug the gadgets unnecessarily, since the only issue I've had is my GPS power cable broke down because of repetitive unplugging (I prefer to remove the GPS from the car when I leave it on the streets overnight). Not that it proves anything, but I suppose it stands as confirmation for the things said above.


It's not an easy yes/no answer. In general it should be OK to leave your devices plugged in.

That being said, a cars electrical system is one of the nastiest places to connect electronics. There are voltage spikes, voltage dips, electromagnetic noise of all kinds and worst of all load dumps.

The safety of your electronics really depends on two factors. First, the condition of your electrical systems and battery. If you alternator fails it may create a huge spike in the system frying anything that's not well protected or unlucky. The battery not only starts your car but when the car is running it acts as an electrical "shock absorber" helping to stabilize the electrical system from spikes and dips. If the battery is marginal or the plates are sulfated it may not reduce a spike as well as it should. Second, is the quality of your devices car charger. The charger should have built in filtering and spike protection. If it's a crappy charger then all bets are off.

It's really your decision whether you want to leave your electronics plugged in or not. There is some minisclue chance of something bad happening and if your electronics are unplugged they are safe but how much time will you waste unplugging and plugging things in being afraid of that event?


To simplify it 'No'. It's best you let your car idle for 20 to 25 seconds prior to shifting up or down. Allow the engine oil to lubricate, and other fluids to start flowing. A minute or two of driving under 2000 RPM should be followed. At this point connect all your gadgets and turn on the AC/heater.

It's a question of stability and durability vs pushing things. People will argue using the amperes or voltage to justify, but this has been long practiced and advised by engineers.

Think of this as having a supply of 1 kilo watt, and you adding things one by one to the battery versus jumping the wagon and adding everything at once.

Would you eat one bite at a time or 54 bites of the same portion together every time? Again the choice is yours, on how you decide to go about this. This is not my 2 cent advice. It's mere facts. Take it as you like and research further with evidence to disprove this.


To answer the question in the title, it does depend on thr car as some cars disable the auxiliary feed during the starting operation - easily noticed as the radio also goes off.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .