Matthew Zieminski is in charge of Supply Chain Quality at Puls and has been in the electronics repair industry for seven years. A version of this article was published on Medium.

Picture this: The sun is shining. The birds are serenading you from the tree you just parked under (They’re going to carpet bomb your car with crap later, but you don’t know that yet.) You’re almost through a long list of errands. And way to go, you. You’re being very productive. You whip out your iPhone for a celebratory selfie, when you see it: a red bar on your battery indicator. Only 10% power remaining.

Panic sets in. You’re not just gonna stand by and let your iPhone die, are you? Scanning the parking lot, you spy a gas station in the corner of the parking lot. Saved! Why not pop in and pick up a lightning cable?

I’m here to tell you … please don’t.

I know those cheap power bricks are tempting. But if it seems too cheap to be true, it probably is. You may save money in the short-term, and it might temporarily save you if you’re desperate, but you’ll eat the cost on those cut-rate cables eventually—because cheap chargers can kill your iPhone.

An ounce of prevention is worth a pound of cure

Damage linked to bad charging cords is pretty common. A post on this issue in the iFixit Answers forum has over 45,000 views—and that’s just for the iPhone 5c.

Of course, the easiest way to avoid damage from bad charging cords is to only use good chargers. But in a market saturated with Apple accessories, how do you differentiate the good, the bad, and the ugly?

Easy rule of thumb: Look for accessories with an MFi certification. MFi stands for “Made for iPhone, iPod, or iPad.” (There should be a sticker on the package that says exactly that). MFi is a licensing program ensuring all those third-party accessories are actually designed to work—under Apple’s specs—with your iDevices.

The MFi program was introduced in 2005. At the time, the press denounced MFi as a gimmick—an attempt by Apple to make companies pay for the privilege of making accessories. But Apple’s top brass argued that the program was a way to standardize how accessory-makers work with Apple products , while also preventing consumers from getting stuck with bad knockoffs. I don’t think all accessories need to be Apple-approved, but when it comes to charging cables, I’m inclined to side with Apple on this one.

These days, you can’t throw a rock without knocking a cheap iPhone accessory off a store shelf somewhere. Some of those aftermarket accessories are pretty innocuous, like a third-party watch band and a not-so-Apple iPad case. Are you gonna destroy your devices with those non-MFi-approved products? Probably not.

A knock-off charging cord, on the other hand, can do some serious damage. Because those little ne’er-do-wellers want to give your phone unlimited power. Emperor Palpatine jokes aside, your iPhone can’t handle that much juice. Eventually, a bad charging cord can burn out a very important chip on your logic board called the Tristar (or U2 chip). The damaged Tristar seriously impairs your phone’s ability to properly charge.

Trent Denison of the repair site, Rice Is For Dinner, lists some of the most common symptoms linked to a damaged Tristar chip:

• “Not charging (no explanation necessary)
• Fake charging (shows it’s charging with a lightning bolt, but % doesn’t change)
• Various iTunes errors which indicate USB interruption
• Charger won’t/can’t charge a battery that’s “dead”, but will charge or partially charge a battery that isn’t “dead”.
• Battery suddenly drops from a higher % to a lower %
• Battery charges to a certain (random) % then stops
• Battery drains to a certain (random) % then dies (phone shuts off)”

Importantly, changing out the battery or charging port won’t remedy the issue, because the problem is on the motherboard.

Why knock-off cords fry your iPhone

When I get asked if buying a $19 charging accessory is really necessary, I have but one answer. You betcha. Real lightning cables prevent your iPhone from fying.

Jessa Jones, of iPad Rehab and an all-around repair badass, puts it like this:

“The MFi cables are important because those have a chip inside the cable that will protect your device from voltage fluctuations that will kill the device.”

MFi cables are designed to work with an iPhone. The Tristar (or U2 chip) regulates the amount of power that your phone’s logic board can receive. A bonafide MFi charger has what’s called an E75 chip. The E75 is like a bouncer. It scans the crowd outside of the door, makes sure everything is chill, and then tells your phone that it’s okay go ahead and take in the voltage. Then, the E75 validates the message with a super-secret password. If you plug in a cord that doesn’t have an E75, you’ll see a “Accessory not supported” message on your phone. No password, no charging.

Naturally, entrepreneurs in certain parts of the world have reverse-engineered that E75 component to make a cheap, knockoff charging cable. The fake E75 chip tricks Apple by acting like a high schooler with a fake ID. Then things get rowdy. The cheap charger routes unregulated power into the device—which can destroy the Tristar chip and causes the aforementioned battery woes.

The cheaper the charging cord, the more likely it’s a shady charging cable that will eventually fry your phone.

“A bonafide [charger] with the E75 chip will cost you $4 plus whatever it costs to make the cable, plus profit,” Jessa points out. “So the cheapest that anyone would legitimately sell this certified board would be, maybe, $5.”

Jessa’s point here is that if you find a charging cable for sale for under $5, you’re playing with fire. It’s almost certainly a knock-off. Even a $5 charger is a gamble. Many non-MFi accessory-makers slap a fake MFi sticker on their products—even though they’re not accredited. So, your safest best is to go through trusted, verified sources to get your accessory fix.

If you think you’ve already damaged your phone due to a bum charging cord, I’m afraid there’s no good DIY fix. As I mentioned earlier, swapping out the battery or changing the charging port won’t work. It’s the motherboard that needs a little TLC. The Geniuses at the Apple won’t be able to help, either—they can’t make repairs to the motherboard. So if you don’t want to be stuck buying a new phone, you’ll have to go to an independent repair shop that offers microsoldering services. They’re the only ones who will be able to revive a mangled motherboard.

Of course, it’s much easier to just avoid knock-off chargers in the first place. No knock-off = no damage = no need for a repair. So next time you’re thinking about plugging a sketchy cord into your $700 iPhone—just put the cord down and walk away. Those cheap cords are way more trouble than they’re worth.