Finally, someone made it!
Constant 1.5v (Ni-Mh is 1.2v):
https://www.aliexpress.com/store/product/4pcs-1-5v-2800mAh-AA-rechargeable-Li-polymer-li-ion-polymer-lithium-battery-4-slots-USB/314368_1280101221.html?spm=2114.12010612.0.0.wq3PFS
My RC car would love these lol:
https://www.amazon.co.uk/gp/product/B0155X5SYY/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1