Why is my battery draining faster after updating to macos ventura 13.4.1?

The update of Ventura will be re-indexing ALL the changes that have occurred.

That would be normal.

Depending on the amount of changes / data on the computer, it could take a day or maybe more for it to finishes.

Suggest keeping the computer plugged into the charger for maybe 2 days.

This may not make the re-indexing move any faster but it will not place undue use on the battery.

There after, the battery should return to normal when not running with the charger attached to the machine

Are you solved? Or did you downgrade to Monterey?