The MIC2251 based boost converter died pretty quickly on NiMH, so on to another one.  With amazon shipping now taking 2 weeks, is it still economical to buy a pack of 5 breakout boards for $10 just to get 1 you need?  There are boost converters based on the ME2108 which convert .9V to 5V.  

https://www.amazon.com/gp/product/B07L76KLRY/ref=ox_sc_act_title_1?smid=A1IU4FC9F8Y7P1&psc=1

This is not to be confused with the ADP2108A which is a buck converter.  There is an annoying trend of Chinese companies copying part numbers of western parts for different functions.

There are better boost converters for making 5V from .6V.

https://www.mouser.com/ProductDetail/Nisshinbo/RP401N501C-TR-FE?qs=ilL34mSzaLh3V8pLMUWh%252BQ%3D%3D

Another solution is whacking in a 3rd battery & running it on 3.3-4.5V.  There's no single AAA holder & no easy way to run to Radio Shack to get one.  There are scenarios where the metal parts are extracted from a $1.25 store flashlight & repurposed in a printed holder.  That would entail printing a new enclosure, repositioning the magnets & hall effect sensor, increasing the resistors.

The cheapest solution is whacking in a lipo & running it on 3.3-4.2V like everything else.  These applications tend to be single use, but lions have tons of unused lipos.  The lipo goes down to 3.3, puffs, & is thrown away.

In went a puffed one dating back to 2015.  It has every intention of never being replaced & outlasting the remote control.