Mine is not comparable with the Early Kindles but it comes close to the Oasis with the tiny Battery. I have to charge it every 1 - 2 Weeks. Wifi is disabled, Bluetooth turned on. I only use the Koreader App, sometimes Wikipedia.
Powersafe triggers after 24h of inactivity what really rarely happens because I read every evening.
Was in the same situation last year and gave up waiting for a new Oasis or Voyage. Bought an Android Reader (Boox Go Color 7) with Buttons. Battery life is comparable to the Oasis, Buttons are OK. The Oasis is much better made. I really enjoy the App Koreader and the support for Bluetooth Remotes. I transfer my Epubs remote via Calibre.
OT: How happy are you with the Note Air 3C? How long last the battery? Any Problems with the build quality? I've read a lot bad stuff about the device and have mixed feelings