I want to use this LiIon battery (this one seems like the same one but in the UK) with ESP32 Feather however I'm not sure whether it's safe to do so. I'm confused because Adafruit's docs say "LiPo" everywhere on the product pages and throughout this power management guide, however they do mention LiIon once at the beginning:
Which leads me to think that since the battery I linked is also 3.7V/4.2V it should be just fine.You can also connect a 4.2/3.7V Lithium Polymer (LiPo/LiPoly) or Lithium Ion (LiIon) battery to the JST jack.
However at the bottom in alternatice power options there is no mention of LiIon:
I have some very tight space constraints yet a relatively power hungry application. I previously used Arduino Nano with a 9V battery but moving to ESP32 for Bluetooth and WiFi + easy way to add rechargeable battery.For mobile use, where you don't want a LiPoly, use a USB battery pack!