xbox one battery pack

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?

To resolve this issue, determine the faulty component and then replace that component:

The Xbox One Wireless Controller

To troubleshoot the wireless controller, try using AA batteries, or try a different Xbox One Rechargeable Battery Pack to verify that nothing is wrong with the controller. If the controller works with different batteries, it isn't causing the issue.

The Xbox One Play & Charge cable

To check whether the cable is the problem, try a different Play & Charge cable (or any standard USB to micro-USB cable) to charge the battery. If the battery charges correctly with a different cable, your charge cable is faulty.

The rechargeable battery

To troubleshoot the rechargeable battery, try the following:

Use a cotton swab and some isopropyl alcohol to clean the four gold contacts on the Xbox One Rechargeable Battery Pack and on the Xbox One Wireless Controller. Then try to charge the battery again.

Try a different Xbox One Rechargeable Battery Pack with the charge cable. If the second battery charges correctly, your original battery is faulty.

To resolve this issue, determine the faulty component and then replace that component:

The Xbox One Wireless Controller

To troubleshoot the wireless controller, try using AA batteries, or try a different Xbox One Rechargeable Battery Pack to verify that nothing is wrong with the controller. If the controller works with different batteries, it isn't causing the issue.

The Xbox One Play & Charge cable

To check whether the cable is the problem, try a different Play & Charge cable (or any standard USB to micro-USB cable) to charge the battery. If the battery charges correctly with a different cable, your charge cable is faulty.

The rechargeable battery

To troubleshoot the rechargeable battery, try the following:

Use a cotton swab and some isopropyl alcohol to clean the four gold contacts on the Xbox One Rechargeable Battery Pack and on the Xbox One Wireless Controller. Then try to charge the battery again.

Try a different Xbox One Rechargeable Battery Pack with the charge cable. If the second battery charges correctly, your original battery is faulty.

IHIGHLY recommend the Energizer charging stand! I had it for the 360 and I have it for the One. It works amazingly and it comes with two battery packs.

Adept,

Microsoft sells 2 docking station chargers on their store:

Energizer 2X Charging System for Xbox One

Nyko XB1 Charge Base for Xbox One

I have used the Energizer system almost since Day 1 and have had no issues and very happy with the purchase. Dual charging, no cables to connect the station to the controller, easily docks, and holds the charge for days. Hope this helps!