Can I use Mobile ID if my phone’s battery is dead?

If you have any of the iPhone XS, XS Max or XR models or later, YES. Express Mode with power reserve is available for up to five hours when your phone needs to be charged.  Android phones and other iPhone models (iPhone 8 and earlier) do not offer this feature.

For more details, see https://support.apple.com/en-us/HT208965