X220i here, and even though modern browsers and applications do tax its CPU (leading to shorter battery life), I still get at least 5 hours out of a new (and inexpensive) 9-cell battery. Build quality is simply second to none, the hinges are still perfectly tight with no slop, even after 7 years.
I have one of those from work and running NixOS in it, everything works perfectly and I love the machine.
Btw if thinking of a X1C for Linux use, I'd skip the latest for now due to them changing how the sleep works and it having issues even with Windows (losing battery while sleeping). The fifth model is great though, if you're not looking for the 8th gen CPU and HDR screen.
x220 user myself, great little machine. Hard to break. I upgraded the disk, 16 GB RAM and new battery. I once dissassembled it completely to replace the CPU thermal paste and was surprised by how easy it was. Now I'm confident that whatever breaks I'll just fix it.
