Double AA Fake Battery to use Vape LiPo battery to power Double AA devices.
I use a diode in series to drop slightly the voltage. I don't have the diode ref, but I just use a diode with à 0.6V drop voltage (checked with a multimeter).

I added to the Lipo a protection circuit taken from an old lipo battery (the vape battery doesn't have those), but that can be found easily on AliExpress