I've purchased a ZenBook 14 OLED 2023 (with i5 1340P).
The model number is UX3402VA.
Initially it was giving me up to 9 hours of backup in light usage (5-6 chrome tabs, Spotify) at 30-40% brightness. But after I updated it to the latest BIOS firmware (version 302) and Windows update (version KB5026372), battery backup has become almost half. Now it won't last more than 5 hours on full charge, which is a shame considering my friend's last gen Vivo Book S14 is giving same backup with a H series processor, with similar usage. Another friend of mine who has the ZenBook Flip (same specs), has no issues with his unit. That one is giving 8-9 hours backup.
Please fix the issues and update the software so that I can get back my expected battery life, otherwise what's the use of buying ZenBook with P series processor if it won't last longer than a Vivo Book with H series processor.
I've happened to have the same problem, but with UM3402YA. After upgrading BIOS 300 -> 305 battery drain increase significantly. I got 4-5 hours of office work instead of 10-12 on stock BIOS version. And now I'm not able to downgrade because this piece of garbage asus website doesn't allow me to download previous BIOS version from here - https://www.asus.com/laptops/for-home/zenbook/zenbook-14-oled-um3402/helpdesk_download/?model2Name=U...
If I click on BIOS/Firmware link it redirects to https://www.asus.com/laptops/for-home/zenbook/zenbook-14-oled-um3402/helpdesk_bios/?model2Name=UM340... which doesn't allow to download any BIOS.
Honestly, I completely regret I bought this ASUS laptop. That a total disaster with non-working speakers. Of course I read that quality of ASUS products dropped down, but didn't realize how much.