There are semistandard cylindrical Li-ion cells. Common sizes include 14500 (14x50mm; AA-size), 18650, and 21700. Many devices with built-in or proprietary batt

There are semistandard cylindrical Li-ion cells. Common sizes include 14500 (14x50mm; AA-size), 18650, and 21700. Many devices with built-in or proprietary batteries use these cells, but it seems like flashlights are the only category where they're usually removable and not housed in a proprietary case. I've owned bluetooth speakers and handheld fans that run on a single 18650. For many other product categories, the reasons they don't are mostly counter to the interests of consumers, but market demand doesn't seem to be strong enough to change this.