My venu sq 2 battery drop very fast in this werk, the battery drop 50% less than 24 hours

Mine too. Tried hard reset already but didn't help. I believe it's firmware problem as it's just suddenly happened in the past 2 months or so.

Garmin's planned obsolescence?

There has not been a firmware update for this device since June so there is most likely another factor. I would recommend reviewing the article Tips to Extend the Battery Life on a Garmin Fitness Watch and review the settings. Especially any app installed from Connect IQ. It that doesn't improve battery life again please reach out to Garmin Support for assistance

I did a hard reset to clear off everything. And the only app I have reinstalled back are Garmin apps Hydration and Calculator. Nothing else. Still the same battery drain issue.

Perhaps that's about the lifespan of a 2 year old venu SQ2 ??? Which sucks!!!

However since the June major update, there have been a couple of minor updates. I recall a BLE Software update. Another I can't remember. These minor updates could have messed things up.