1 Which phone do you have?

2 Your charger

Which port is your cable plugged into?

Many chargers have both – what counts is the one the cable is in right now.

3 Check the cable

For this test your phone must be at 40% battery or lower right now. Otherwise it's pointless – above that the phone throttles itself, and you'd be measuring the throttling instead of your cable.

Enter your battery level now – that starts the clock.

Plug in the phone, screen off, leave it alone. Using it skews the result.

Battery level now (%)

Why is my phone charging so slowly? The four bottlenecks

Almost every smartphone can charge faster than it does day to day. It's rarely the phone's fault. It's one of four bottlenecks between the wall outlet and the battery – and Charge Check tests them in this order.

1. The charger doesn't have enough watts

An iPhone 15 takes up to 20 watts, an iPhone 17 Pro up to 40, a Galaxy S25 Ultra 45 watts. The old 5-watt cube or a 12-watt tablet charger delivers only a fraction of that. The wattage is always printed on the label, often in small type as "20W Max" or as an output line like "9V⎓2.22A". Charge Check reads the label from a photo.

2. USB-A instead of USB-C

The wide, rectangular USB-A port can't do Power Delivery, the protocol phones use to fast-charge. No matter what wattage the charger claims: over USB-A you get about 12 watts at most. Fast charging only works when the cable is USB-C on both ends (USB-C to Lightning on older iPhones).

3. The charging protocol doesn't match

Samsung and Google only reach full speed with PPS (Programmable Power Supply), an extension of Power Delivery. A 45-watt charger without PPS charges a Galaxy S24 Ultra at 15 watts instead of 45 – and many chargers, big brands included, only do PPS at 3 amps instead of 5, which caps Galaxy models up to the S24 generation at about 27 watts. Xiaomi and OnePlus use proprietary protocols that only the original charger speaks. iPhones don't need PPS.

4. The cable or the charging port

A damaged cable, a cheap cable without the required resistor in the plug, or a Lightning cable without MFi certification throttles charging. Even more common: lint in the charging port that keeps the plug from seating fully. You can't see this bottleneck by looking at the accessories. That's why Charge Check offers the test: from the battery size, the charging power and the phone's charging curve it predicts where the battery level should be after 15 minutes. If you're well below that even though charger and protocol match, only the cable or the port is left.

What Charge Check is not

Not lab equipment. The test is an estimate over the measured period, calibrated against manufacturer claims ("50% in 30 minutes") and real measurements from The Case Tester channel. It reliably tells you whether your setup is in the expected range – not the peak power to the exact watt.