How can I check battary health

If your device is running iOS 9 or below, you can try using a battery health checker app, however, don't try it if you're using iOS 10 or 11, Apple has removed most of the features that allow these apps to work. In the upcoming iOS 11.3 update, you will be able to check the health of your battery. For now, though, you can't really do that accurately.

There is an app called "Battery Life" available in the App Store.

Other than that there's an application called coconutBattery for Macs that will tap into the battery stats including manufacturer, manufacture date, current input power, temperature, (accurate) remaining capacity, and accurate full capacity. Someone mentioned a similar application for Windows, but I don't recall the name.

https://www.coconut-flavour.com/coconutbattery/