There is no current way to make a battery more reliable. It is very often the component that needs replacing. The other component would be the screen. Other than that there's not much across devices that fits "maintenance parts" categories as everything is at such a scale that it would be nearly impossible for a human to fix most things on the board, which is why they typically replace whole boards. Cell phone sales have dropped precipitously in recent years as innovation has slowed down. I don't expect folding phones to be the new hotness, rather an oddity, however the tech might make screens more durable which is a huge plus, batteries on the other hand are limited by physics, so we need replacements or new tech that lasts longer but provides the same or more power.