If you’re using an old charger with a new phone, be sure to check the compatibility. If the charger doesn’t work with your new phone, you may have to buy a new one.

You Can Charge a New Phone with an Old Charger

The sales guy at the phone store might insist you need the newest and greatest charger for your new smartphone, or some fate might befall your pricey new purchase, but that’s not the case.

You can charge your brand new iPhone with the dusty old basic Apple 5W USB-A power adapter that came with your old iPhone 6. It’ll deliver a simple and slow charge that will get the job done. The same goes for nearly every other phone on the market.

Maybe your old Samsung phone had a micro USB port and your new Samsung phone has a USB-C port—so you’ll need a USB-A to USB-C cable to connect your old charger to your new phone—but it’ll work fine.

In fact, you could even argue that using an older charger is better for your battery. The slow-and-low (temperature) approach to battery charging keeps batteries healthier for longer. After all, heat is the enemy of electronics, especially batteries, and the faster you charge a battery, the hotter it gets.

However, fast charging does use a routine to help protect the battery. And we do recommend people just enjoy their phones and use them the way they want to use them without stressing about battery preservation myths and half-truths.

The only pressing exception to our advice that it’s fine to use your old phone charger with your new phone is if your old charger isn’t a high-quality charger but some questionable no-name gas station charger you picked up in your travels.

Continuing to use an older charger from a reputable company like Apple, Samsung, Anker, or such is one thing, but we don’t recommend pairing a dubious $4 gas station special with your brand-new phone. And that’s just good practice all around for all your gear—cheap no-name USB chargers are a fire hazard.

But You Miss Out on Fast Charging Benefits

Even though your old phone charger is capable of charging your phone, you might not be happy with the speed with which it does so.

Although charging time doesn’t matter if you’re plugging in your phone at bedtime every night—whether it takes 60 minutes to charge your phone or 6 hours is irrelevant when you’re sleeping through the charge cycle—it matters a lot more if you want to take advantage of the fast charging options built into modern phones.

You’ll never be able to fast charge your shiny new iPhone or Galaxy Ultra using a basic old 5W USB charger. The older charger doesn’t have the right hardware, can’t deliver the power at a higher rate, and you’ll be stuck with the slower charge rate.

But if you upgrade your charger and pair it with an appropriately sized fast charger, you can charge your phone many times faster than you could with an old 5W charger. Results vary based on your phone’s hardware and the charger you use, but even upgrading from the basic 5W model to a 20W model like this Anker USB-C 20W charger can cut your charging time in half.

More importantly, get you up to 50% battery faster so you can get out the door with enough juice to make it through the day—even if you forgot to put your phone on the charger the night before.

So if you’re a creature of habit who uses their phone roughly the same amount every day, puts it on the charger at the same time every night, and has no complaints about using your old phone charger, it might be fine to skip the upgrade.

But given what a headache it is to be without your phone or left with a seriously depleted battery when you really need a full tank to get through what you have planned for the day, it’s worth picking up one of the many reasonably priced fast chargers on the market.

Even better, if you invest in a beefier charger that can deliver power beyond what your phone requires, like this 100W Anker model, you’ll be able to charge your compatible laptop and other USB devices using the same charger.