iphone battery diagnostic tool

Apple Support has a tool, you can contact Support and they can email you a link. You click on it, and it will test the phone's battery and you will get a response. There is no other diagnostic. There are some battery apps in the App Store, but to get a true idea and to see about a battery replacement through Apple, you need to use their tool.

You're welcome. I use an app called Battery Life, which does provide some information about the battery, however one would need to understand what is being shown to determine what effect that has on the battery. Depending on the age of the device, it is probably not the battery that has the problem. If this just started, it is very possible that in conjunction with the iOS update, a process has gotten stuck, or some corrupt data has affected it. Not knowing what version of the iPhone you have, it is hard to tell. But Apple is still the best bet. If you find the battery is still good, then you need to troubleshoot your apps, etc..