Ask HN: What can you realistically manufacture in your garage?
Have you ever seen a MagLite flashlight? (Or a clone)? The batteries are kept in place by a threaded cap which is spring loaded. My neighbor manufactures the caps, alone, in his garage. Cuts the threads and installs the spring. As far as noise I do hear his air compressor occasionally. You can buy quiet air compressors but they are orders more expensive than a standard unit.