@stib you can recharge the li-ion batteries using a TP4056 charging board, then use the batteries for whatever you want. I get these boards in strips of 5 from Aliexpress, for a couple of euros, including post.

I re-use found vape batteries in my Bluetooth receiver projects...I get the Bluetooth module board for €1.50 of Aliexpress and with the TP4056 and an old vape battery can make a nice rechargeable unit that is the size of a matchbox for a few euros.