Does your iPhone battery drain too quickly or does it not charge when using a lightning cable? Try restarting it first. You can also learn tips to extend the battery life of your iPhone. Are you having trouble getting your iPhone to power on? First, make sure you've given your iPhone's battery enough time to charge. If your iPhone has been without charge for while, it will take more time than normal before it registers that there is any charge in the battery.
If your iPhone is not charging, try to use a different cable and power socket. If you normally charge your iPhone by plugging it into your laptop or MacBook, try plugging it into a USB charger that is connected to the mains electricity. Not all USB chargers are the same too. So make sure that you are using a good quality one, with at least 1amp output - 2amp is better.