How to test an older phone charger safely
Compare an older phone's charging rate safely, separate charger and cable issues, and learn what a browser test can and cannot tell you.
Your older phone charges slowly, or you want to know whether a replacement charger is working as it should. A slow percentage increase does not automatically mean the charger is faulty: the phone, cable, battery condition, and charging level all affect the result.
Use the Charger & Cable Test to compare charging speed in percent per minute. The test is a check of charging behavior, not a measurement of electrical safety or the charger's wattage.
Test the charger and cable
- Open the Charger & Cable Test on the phone you want to check. This tool appears only when the browser reports battery information. If it is unavailable, the browser cannot provide the data, so that alone does not mean the phone or charger is broken.
- Before plugging anything in, check the charger, cable, and phone port for fraying, bent parts, corrosion, or other visible damage. Use a charger and cable that are made for the phone or from a reputable brand. Do not test equipment that is damaged, wet, or unusually hot.
- Connect the charger directly to a wall outlet and connect the phone. Keep the phone in a safe, dry place on a firm surface. Stay nearby while it charges, and stop if it becomes unusually hot, smells strange, or makes a new buzzing or crackling sound.
- Note the battery percentage and the test's reported charging rate. For a useful comparison, begin around the same charge level each time, such as 20% to 60%. Avoid comparing one test near empty with another near full, because phones often slow charging as the battery fills.
- To compare chargers, keep the same phone and cable and change only the charger. To compare cables, keep the phone and charger the same and change only the cable. Let each run for about 10 to 15 minutes, with the screen off and no demanding apps running.
If the phone or charger becomes too hot to comfortably hold, disconnect it if you can do so safely. Do not continue a test just to collect a longer reading.
What the result means
The charging rate is steady and the percentage rises
The phone is receiving charge. A lower rate than you expected may be normal: an older phone may support a slower charging standard than a newer charger can provide, and an aging battery can change how the phone manages charging. Compare results under the same conditions rather than expecting every charger to produce the same number.
One charger is slower with the same cable
The charger may be incompatible with the phone's preferred charging standard, or it may be wearing out. Try a charger recommended for that phone. If a known-good charger is consistently faster under the same conditions, stop using the slow charger if it also gets hot, makes noise, or has visible damage.
Changing the cable changes the rate
The cable may be damaged, unsuitable for charging, or unable to support the rate the phone and adapter can use together. Replace it with a reputable cable that fits the phone. A cable that works for basic charging is not necessarily capable of the phone's fastest supported rate.
The reading is low or changes between tests
Battery percentage is rounded, and the charging rate can change with battery level, temperature, screen use, and background activity. A short test or a one-point percentage change is not enough to identify a fault. Repeat the comparison at a similar starting percentage, with the screen off and the phone cool.
The test cannot read battery information
Some phone browsers do not report battery details to websites. The test cannot estimate the charging rate without that information. Check whether the phone's own status display says it is charging, or compare the battery percentage over a longer period without using the phone.
How to troubleshoot slow charging
- Use a known-good charger and cable. Try a charger and cable intended for your phone, changing one at a time. This helps you identify which part affects the result.
- Check the outlet and connections. Try a different wall outlet and make sure both ends of the cable are firmly connected. Avoid loose adapters or damaged extension cords.
- Let the phone cool and reduce its workload. Close games, navigation, video, and other demanding apps, then leave the screen off during the comparison. Phones can slow charging when they are hot.
- Look for battery health information. On an iPhone, check Settings › Battery › Battery Health & Charging, if that option is available on your model and software version. On Android, open Settings › Battery; the available battery status details vary by manufacturer. A worn battery can make charging behavior less predictable.
- Check the charging port without probing it. Look for lint or damage using a light. Do not insert metal objects, add liquid, or force the cable into the port. If debris is packed in or the connector feels loose, ask a repair shop to inspect it.
- Restart the phone. A restart can clear a temporary software problem. If the phone still charges slowly with a known-good charger and cable, check the phone maker's support guidance or arrange a repair inspection.
When the phone or charger may be unsafe
Stop charging if the phone's battery is swollen, the screen or back is lifting, the charging port is damaged, or you notice smoke, a sharp chemical smell, or unusual heat. Do not press a swollen phone flat or keep testing it. Disconnect the charger only if it is safe to do so, keep the device away from flammable materials, and contact the phone maker or a qualified repair shop. Replace a damaged charger or cable instead of trying to repair it yourself.
What this test cannot measure
The Charger & Cable Test reports charging speed as a percentage per minute when the browser can read the phone's battery data. It does not measure the electrical power in watts, verify that a charger meets a safety standard, or prove that a battery is healthy. Percentage readings are especially rough on older phones because the battery gauge itself may be less accurate.
Use the test to compare two setups on the same phone, not as a safety certification. If the phone behaves normally but charges more slowly than a newer device, its supported charging rate may simply be lower.
