They were replaceable in the old Norelco shavers. It required soldering. If you're 3D printing then soldering is on the same level of technical skill. There's even a solder bridge to disconnect the battery.

Also, allow the blades on the newest model to be reversed. The old version could be reversed, so when the leading edge got dull, you could flip it around.

With the newest version, it's nearly impossible to use the back edge because of the curve of the handle. Clearly designed to reduce blade life by half.

Dude, Just buy a a Wahl clipper set and avoid that headache.

Mine has a big beefy wall-plug one, and one that runs off two AA batteries. Also sturdy as fuck and I've abused and misused the damn thing for like 15 years and they are both still going strong.

I just don't buy battery operated stuff that doesn't have to be battery operated. That's why my bathroom has electrical outlets. K.I.S.S. principal.

My braun has a replaceable battery, it's a li-ion 14500 (AA size but 3.7V), they're a couple bucks.