My iPhone 7 plus is charging very slow

If your device won’t charge or charges slowly

If you have very low battery and plug into power, a black screen or a black screen with a red battery might appear for a few minutes. Follow these steps and try again after each:

1. Check your charging cable and USB adapter for signs of damage,* like breakage or bent prongs. Don't use damaged accessories.
   
2. Use a wall power outlet and check for firm connections between your charging cable, USB wall adapter, and wall outlet, or try a different outlet.
3. Remove any debris from the charging port on the bottom of your device, then firmly plug your charging cable into your device. If the charging port is damaged, your device probably needs service.
   
4. Let your device charge for a half hour (If your device is unresponsive afterward, learn what to do).
5. Force restart your device: Press and hold the Sleep/Wake and Home buttons at the same time for at least 10 seconds, until you see the Apple logo. Then let your device charge for another half hour.
6. If your device still won’t power on or charge, take your device, charging cable, and charging adapter to an Apple Retail Store or Apple Authorized Service Provider for evaluation. You can also contact Apple Support.

*If you're unsure about whether an accessory is damaged, take it to an Apple Retail Store or Apple Authorized Service Provider for evaluation, or contact Apple Support.

3 hours is about right if you are using the iPhone cube that comes with the phone. It will charge slightly faster with an iPad 12W adapter, rather than the 5 watt cube. Not a big difference; perhaps 30 minutes less, because most of the time charging is at a lower current (80% to 100% will take most of the time).

If you have background apps running or are using the phone while charging it will also take longer.

Yes you can use an iPad charger to charge your iPhone. It won't make a huge difference as Lawrence indicated, but it also will not hurt your iPhone. It will only use what it has the capacity to use.

Cheers,

GB

That's how long it takes. It is not slow for an iPhone 7.

Cheers,

GB