So? Just wait and see how many flights you get before you have to recharge your battery. I wouldn't want some clunky external battery hanging off the back of my TX.
When you spin it by hand does it feel gritty or different from the others? You got an outdoor hose with a sprayer? Cover the the main body with some plastic, then fire it up and blast the offending motor a few times (while it's running) from the top. Spin it by hand again and see if it...
Holy Stone is not a manufacturer/cloner, they just rebrand (usually older) offerings and tend to charge a premium price.
About $46 here.
https://www.aliexpress.com/item/Dron-JJRC-H12C-DFD-F181-FPV-4CH-2-4GHz-Quadcopter-Drones-Remote-Control-Helicopter-With-5MP/32580037748.html
Sorry Neil, they use an XT30.
You need one of these Tom.
https://www.banggood.com/XT30-Connector-to-Banana-Plug-4mm-Battery-Connectors-Charging-Cable-12CM-p-1083401.html?rmmds=search&cur_warehouse=CN
Or better yet this you can do multiples too...