Suburban Chicago since 1981.
Historically I’ve tried to buy replacement batteries directly from Lenovo whenever possible, as I tend to think of the device’s manufacturer as the most reliable source of its batteries. However, I’ve used encompass.com for replacements on numerous occasions, and have found them to be equally reliable (though they have been slow on occasion).
After seeing some of Craft Computing’s videos on YT I’m considering getting my hands on one of those cheap Erying mainboards off Aliexpress with a laptop CPU on it. Seen those as low as 140 bucks with a 13th-gen i5, just add a cooler and desktop DDR4.