Confirm which model of Dyson vacuum you have (like for me I have a V8 model) and find the battery adapter that matches. Like if you have a V6 and want to use your Bauer batteries, lookup something like "Dyson V6 battery adapter for Bauer batteries" - seeing as Bauer batteries are Harbor Freight's version of someone else's battery, you might need to do some digging to make sure you get the right one.

It's like 3 screws to take the OEM battery out, you put the battery adapter in its place (using the same 3 screws), and then slide the battery on and off just like your other cordless tools. It's pretty awesome.