Charging ipad is slow

What model iPad do you own?

Your signature states it is still running iOS 10.

If this is correct, you have an older, over 6-year old iPad 4th generation.

If this is, also, correct, you might have a battery issue.

What wattage Apple power block are you using?

Do you have another cable and comparable Apple power block you can test with?

Try either quitting all apps in the iOS App Switcher and turning Wifi OFF and try and charge the iPad.

OR

Shut down/off the iPad completely and try and charge it.

If still no joy, bring the iPad, charge cable and charge block into your nearest, “local” Apple Store for diagnosis, evaluation and potential options.

Best of Luck to You!

If you are using a regular Apple 5 watt charger (such as for an iPhone) these are pretty slow.

Try turning it off for another hour and let it continue to charge with the power off for a couple hours to see if you can get it to 100%.

Are you using the full-sized 12 watt charger?

Apple 12W USB Power Adapter - Apple