As many of you know…well, the ones of you that follow me on Twitter, at least know that I’ve gone from owning an iPhone 7 to an Essential Phone (basically the co-founder of Android made his perfect idea for a phone) and when I opened the box, the Essential Phone came with a USB Type-C cable to put into the 27 Watt Fast Charger that also came with it.

First few days of it were pretty great, actually. I could use my phone pretty heavily and not have to carry some type of charger with me. Then, some sort of threshold hit with the battery. I don’t know what, I don’t know why. My phone suddenly went from an 18-hour battery to something like a 5-hour battery. Needless to say, I was less than impressed, but given that, I had to carry almost 7,000 mAh of battery capacity in my iPhone 7 just to get me through a day, I wasn’t all that surprised since the Essential Phone has well less than half of that capacity.

So, I did what any normal human being would do. I plugged it into the wall socket, browsed the web on my nearby laptop and waited. The thing was when I checked not even 30 minutes later, the Essential Phone said I had two hours or more to go until I could get it to full charge. That’s not fast charging, that’s normal charging.

If you don’t understand these terms, let me break it down for you: A USB-C cable is just like the normal USB cable you would use on your other Android phones, but it looks more like Apple’s Lightning cable and functions like it too. It’s even got the same shape! With quick charging, it’s basically a fancy way of saying the cable increases the current going from the wall outlet to your phone at a higher rate. Most Android phones have it since most of the internals are manufactured by Qualcomm, which promises an 80% charge in about thirty minutes.

The truth is a lot more complicated. While the combo of fast charging and USB-C can provide that much of a charge in that amount of time, it almost never does. The reasoning for this is a lot more simple: wall chargers can only charge something with as much power that is available to them. So, if you go to a movie theater or most public places, expect to be sitting there for about an hour or two. That’s likely because a lot of people are using a lot of power all at once, so the electrical engineers designed the current going through non-essential outlets to produce less current, thus the longer charge time. The same thing occurs with public Wi-Fi. More people, less power.

So, the next time you see a charger or phone that promises “fast charging” or that USB-C is faster than anything else out on the market, just remember that is a promise that is just a long way to say the cable and technology hinge on your situation.