Does Charging Your Phone In Your Car Ruin Your Battery?

Electricity is electricity - but not all electricity comes from the same place.

It's a bit of an odd question. Some of you with some mechanical and electric experience may already know the answer fairly quickly, while others may be genuinely curious - either way, we're here to answer it: does charging your phone in your car ruin the lifespan of your car's battery?

The short answer: no. The long answer takes a little bit of understanding of how a car's electrical system works - both old school stuff and the modern stuff - and why there may be other considerations beyond your car's battery. Let's dive into it.

For the majority of automotive history, the average car has come with a battery. Yes, it's the big boxy thing that sits in your engine bay or occasionally in your boot, and it's usually the thing you have to change when you try to start your car and the engine just won't fire up. Different types of batteries have different lifespans depending on usage - but it is also a bit of a gamble as some batteries can last as short as six months if you're unlucky.

But that's beside the point. The function of the battery is twofold - the first is to provide the starter motor of the engine with enough juice to get it turning, and the second is to function as a bit of an energy reserve for when you really start to pile on electrical loads.

"A reserve for what?" you might ask. Well, car engines also have something known as an alternator which is driven by your spinning engine via a belt. The alternator works as a little generator, providing electricity as it spins - and this is what powers the vast majority of your car, the vast majority of the time. The alternator also serves to recharge the battery as you move along - if it didn't, your battery would go flat pretty fast.

The battery steps up when the alternator isn't spinning quickly enough and generating enough power to help feed all the various systems, like the fans and the screens, the radios and the headlights - and so on. Rarely is that the case these days, but it's always good to have a bit of backup. 

So by now, you can see that the alternator is what's really doing the heavy lifting - and also why charging your phone in your car doesn't exactly destroy your battery in any particular way. That being said, adding too much electrical load can also be a problem for your car, and both the alternator and the battery may need uprating in the process.

Fortunately for you, charging your phone is one of the smallest electrical loads you can add to your car. Brighter or additional headlights, as well as sound system components like subwoofers, speakers, and amplifiers, are usually the biggest contributions to heavier electrical loads. That's usually the reason why cars with insane sound system setups also need beefed up alternators to cope with the load. 

Sometimes you may also want a larger battery just for the extra juice provided to make cranking the engine a little easier. This isn't something you generally do for your average daily driver unless you really want to get creative with the engine bay, but rather something we do with aftermarket modifications. 

With all that in mind - go ahead and plug in that phone charger without worrying about a thing. But accidentally leaving your headlights on overnight? That's going to be a problem you'll pay for in the morning.