Why is my Photos app draining battery after latest update?

If you just recently updated within the last 3 days, Photos is still reindexing the library for object/face identification and the time it takes will depend on the size of your Photo Library.

I also recommend doing a Force Restart after an update.

If it’s a background activity it’s related to syncing and backing up your photos. If you stop the process, it just starts up again until it’s finished. Normally it does the background activity at night while the iPhone is inactive and won’t interfere with your normal daily activity.

Do you charge your device at night? Do you leave your iPhone turned on at night?

I’d do a forced restart in case a glitch developed in the backup/sync. This can happen for a variety of reasons. Then when you go to bed, leave iPhone turned on and plugged into a charger. Depending on the photos and speed of your WiFi, it will complete in one or two nights.

Are you specifically referring to Apple Photos or a third party app? Which recent update version are you specifically referring to?

Have you done any of the basics like a forced restart of your iPhone?