Your question is related to Using 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
Renewable batteries are being phased out , even in lower end devices, so the usage of that "thing" when 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