iPhone batteries are user replaceable though! Apple will sell you the battery for $91 (only $45 if you send your old battery back) and will rent you all the equipment you need packed in two pelican cases for $49/week, shipping included!
Why is it expected that you should be able to swap an internal component if you haven’t used a screwdriver before? Try swapping the brake pads in your car or fixing a blockage in your dishwasher and you’ll find that fixing the iPhone is comparatively quite easy.
https://support.apple.com/self-service-repair