Hard to do when Apple intentionally slows down the phone with new firmware updates and Android OEMs abandon replaceable batteries for a soldered on unit whose ability to hold a charge drops off precipitously after 2 years.
I've never seen a cellphone with a soldered battery, and most of the slowdown in iPhones is caused by the OS slowing down to make up for reduced battery capacity. With apple and other manufacturers having to replace batteries in their own phones, I seriously doubt we'll ever see soldered batteries.