Yeah, I think for better or worse, the most universal and least consumerist “cordless” system is picking up your favorite used Mains corded tools, and getting yourself a Jackery/Ecoflow/whatever battery bank to plug into. This can be really cost effective for a DIY setup.

FYI KaiOS is spyware garbage moreso than stock Android w/ gapps. Download a GSI rom if you want to run stock android on most phones post Android 8.1