Removeable battery-like "thing" that provide unlimited power for android phones
Your question is related to How to use android phone without battery?

IMO, the "thing" you visualise is "not a thing
" (couldn't resist the pun) , since


Battery is integral to Android device (unlike an accessory) and the designed usage of device - both these are discussed in my answer to question linked above
Removeable batteries are being phased out , even in lower end devices, so the usage of that "thing" even if it exists,  is very limited 


Whether such a "thing" is going to come in any time is open ended but unlikely for reasons above