@steven987 I would argue the perfect battery setup is a single AA or AAA LiFePO4.
No boost or regulator needed, nominal voltage: 3.2v
Much safer than traditional LiPo/Li-ion
Really easy to solar charge with TP5000 module and cheap solar cells
Cons
they're not super available
a little pricier
require a LiFePO4 charger
still potential for fire with enough abuse
Significantly less power density than NiMH or alkaline
LiFeP04 Batteries
https://www.ebay.com/itm/12X-SOSHINE-LIFEPO4-AAA-10440-BATTERY-280MAH-3-2V-FOR-WIRELESS-MOUSE-ALARM-TOY/333294469931?hash=item4d99e6032b:g:lk0AAOSw04ddULoH
TP5000 Charging Module (I use for solar charger)
https://www.aliexpress.com/item/32807030878.html
Solar Cells
https://www.aliexpress.com/item/32882323830.html?spm=2114.12010612.8148356.16.192a59c23u0hej
