battery pack for the xbox one s controller

But then if it;s the wrong battery pack, it shoudn't work with either controller ...the fact it works in one but not the other points to an issue with the second controller

The Xbox One Venom battery pack won't even fit in the Series X controller (or at least not without trimming bits off it)..as the OP can fit the pack with no issue, it suggests it's the right battery pack. Unless Venom have released more than one battery pack for the Series X?

When you say you've tried New battery packs, was it a new battery pack designed for the Series S/X controllers? The Xbox One Venom battery packs won't fit the new controllers (Venom sell newer versions of these). The controller's much smaller size may have necessitated some minor changes?

The Series X controllers available now uses the same official battery packs as the Xbox One and Series S controllers.

They are actually AA, but you need the back cover that came with the controller. :/

It holds the batteries and then you insert that pack on the controller like you would with the recharge one.

This: https://www.amazon.com/Trenro-Black...+battery+pack&qid=1562521277&s=gateway&sr=8-8

My battery pack works with the new controller, but it does not charge like many others. I've tried numerous USB cables. The cables and both battery packs I own work with my old Halo 5 controller, but there has to be a compatibility issue with the One S controller
and its firmware.