After my iPhone dies I get a notification on my iPhone screen stating this iPhone is still findable but when I log onto find my iPhone I cannot locate my device

If the Find My feature is enabled on the phone, you will be able to find the phone using the Find My application on another device using a browser.

If the lost phone is powered off, you will still be able to find the phone on the Find My map.

However, if the battery on the phone has run out, or the phone cannot connect to the Internet where it is currently located, then the phone cannot send out information about where it is located.