That's fair. I'd consider myself fairly new to it all, I'm not passing judgment but it's worth checking out a vid on how to do... If you've used a soldering iron once or twice you could probably handle it.

You may also want to (or have your person doing the work) replace the single-shot resistor fuse with a self-healing one while they're in there. Both parts are on the controller board. The fuse is notorious for blowing, and that can make the whole system unable to detect your controllers.

Rechargeable battery chemistry usually can't exactly match the voltage on the old ones. I've seen problems with all sorts of stuff by switching to rechargeable AAs. They typically have only 1.2v compared to 1.5v of a regular AA.

But the rechargeable coin battery mod for the Dreamcast is fine, I modded mine years ago and have had no issues.

Yeah, there are different models. I have a first gen North American one. I didn't realize some had swappable batteries.