Why a USB cable heats up during long charging sessions

Your USB cable feels warm after charging for a while, or the connector is hotter than the rest of the cable. Some warmth can happen during fast charging, but unusual heat can point to a damaged cable, a poor connection, or a problem with the charger or device.

First, stop charging if the cable or plug is uncomfortably hot, smells burnt, looks melted, or has exposed wires. If it is only mildly warm and undamaged, use the Charger & Cable Test to compare charging rates with another cable. The test reports charge speed as a percentage per minute. It cannot certify that a cable is electrically safe or measure its exact temperature.

Compare the cable safely

Open the Charger & Cable Test on the device you are charging. It appears only if your browser reports a battery. If you do not see it, you cannot use this test on that device.
Check the cable and both connectors before plugging them in. Do not test a cable with fraying, bent parts, burn marks, a loose fit, or other damage.
With the device at a similar charge level each time, use the same charger and outlet to check the cable's reported charge rate. Keep the screen and workload consistent, and stop if the cable begins getting unusually hot.
If the first cable stays only mildly warm, let the device and cable cool, then compare with a known-good cable. Change only the cable, not the charger or outlet, so the comparison is useful.

Charging speed changes as the battery fills and as the device heats up, so a single reading is not a pass or fail. Compare cables under similar conditions instead of treating one percentage-per-minute result as a fixed specification.

What the result means

The cable is mildly warm and the charge rate is similar

This can be normal during a long session, especially when the device supports fast charging. The charger and device pass current through the cable, and some energy becomes heat. If there is no damage, unstable connection, warning, or strong temperature rise, continue to monitor it rather than assuming the cable is broken.

One cable gets hotter than another

If the charger, outlet, device, and starting charge are similar, a clear difference points toward that cable or one of its connectors. A worn or poorly fitting contact can add electrical resistance and generate heat. Stop using the hotter cable, particularly if the connector is discolored or the connection cuts in and out.

The cable stays cool but the device or charger gets hot

The heat may be coming from the battery, charging port, or adapter rather than the cable. A device may also slow or pause charging when it gets too warm. Check whether the device displays a temperature or charging warning, and let it cool before trying again.

The charge rate is low or keeps changing

A slow or variable rate does not prove the cable is faulty. The device may be nearly full, using power while charging, limiting charge speed because of heat, or negotiating a slower charging mode. The Charger & Cable Test is useful for comparisons, but it does not identify the exact electrical cause.

How to reduce cable heat

Unplug a damaged or unusually hot cable. Do not keep charging to see whether the heat gets worse. If a connector is smoking, melting, or too hot to handle safely, avoid touching it and disconnect power at the outlet if you can do so safely.
Check both ends for a loose fit. A plug that wobbles or falls out can make an unreliable connection. Do not force it into the port, and do not scrape the port with metal objects. Have a damaged device port inspected.
Use a cable suited to the charger and device. Replace damaged, very thin, or poorly made cables with a reputable cable rated for the charging system you use. A cable's connector shape alone does not tell you its supported charging speed.
Give the device room to cool. Keep it out of direct sun and off blankets or other surfaces that trap heat. If the device is hot, stop charging and let it cool before testing again.
Check for a device temperature warning. On Windows 11, open Settings › System › Power & battery. On macOS, open System Settings › Battery. On Android, open Settings › Battery, and on iPhone, open Settings › Battery. Menu names and warnings vary by model. If the device says charging is paused or limited because of temperature, follow its instructions rather than trying another cable while it is hot.
Compare with a different charger only after the cable passes inspection. If a known-good cable also heats up with one adapter, stop using that adapter and check its condition. Avoid testing combinations that already show damage, looseness, or a burnt smell.

When the cable or charger needs replacement

Replace a cable that heats much more than a known-good cable under similar conditions, has cracked insulation, exposed conductors, dark marks, or a connector that fits loosely. Do not repair a charging cable with tape or keep using it at a lower charging speed. If the adapter itself becomes unusually hot, is damaged, or makes a buzzing or crackling sound, stop using it too.

If multiple known-good cables and chargers cause the same problem, the device's charging port or battery may need service. Contact the manufacturer or a repair shop, especially if charging repeatedly stops, the port feels loose, or the device shows a temperature warning when it is cool.

Why heat can build up in a cable

Every cable has some electrical resistance. When charging current passes through it, resistance produces heat. A higher charging load, a long or poor-quality cable, or a worn connection can increase that heat. A loose contact can concentrate it at one small point, which is why a hot plug deserves more concern than a cable that is only slightly warm along its length.

The Charger & Cable Test measures how quickly the reported battery percentage rises. It cannot tell you the cable's temperature, confirm its safety rating, or determine whether the heat comes from the cable, charger, port, or battery. Treat physical damage and excessive heat as warning signs even if the charge rate looks normal.