Battery

If the battery is not a genuine battery, then you will see this information. The message will disappear from your lock screen after some time. However, you will always be able to see the message here: Settings → General → About

You can find more information here:

About genuine iPhone batteries - Apple Support

Did you have the battery replaced? If so and it was not by Apple or an authorized repairer that message will appear, nothing you can do about it now.