Recommend a long-lasting battery

[Vitesze]

In a related topic (Powering Electron with LiPo and VIN with Batteries - #3 by ScruffR) @ScruffR mentioned:

@ScruffR

Without having looked into the Electron schematics and any number crunching, I just got the feeling that the AAs would get drained first till their voltage equals the one of the LiPo + 0.2V (schottky forward drop) and then both would get drained in parallel (with the risk of back feeding into the AAs if you don't add a protective diode).
So not what you want to achieve.

So assuming the voltages would be very similar (3.7V for LiPo, 3.6V for Tadiran) this would mean draining in parallel?