iOS 12.4

There is no more reason to believe that iOS 12.4 will correct battery problems than there is to think it was iOS 12.3. that caused them.

You might want to look at these article:

About the battery usage on your iPhone, iPad, and iPod touch - Apple Support

iPhone Battery and Performance - Apple Support

Batteries - Maximizing Performance - Apple

iOS 12.4 is with the following changes.

Phone migration

• Introduces the ability to wirelessly transfer data and migrate directly from an old iPhone to a new iPhone during setup

Apple News

• Makes downloaded issues accessible in the My Magazines section, both online and offline
• Adds all publications in Apple News+, including newspapers, to the catalog at the top of the News+ feed
• Adds the ability to clear downloaded magazine issues by selecting History > Clear > Clear All

Other improvements and fixes

• Includes a security fix for the Walkie-Talkie app on Apple Watch and re-enables Walkie-Talkie functionality

This release also includes support for HomePod in Japan and Taiwan.