While it is of course possible to replace the battery in most phones with specialized tools, for some of the newer models it's very difficult to do without damaging the device. When we're talking about a phone you just bought on eBay with the intention of making it your daily driver, that's a hard sell.

All other things equal, I will always pick the slightly thicker phone with a removable battery over the one that might have me breaking out the spudger.