You could get the slice battery, along with the 9-cell that should bring you to 15 hours at least, and probably up to 20 (provided you get batteries with accurate stated capacity).
Yes, it'll make the laptop significantly more bulky, but the X220 and X230 are from before Lenovo started putting ultra low voltage CPUs in their laptops, so they do have higher TDP than later models. That's just how it is.
The X240 can supposedly go for over 24 hours with the maxed out battery configuration.
I bought an X250 because of that. I hated that machine. It felt so cheap and weak. It did not feel like a thinkpad. Sold it rather quickly even though it was much faster and longer lasting than the X230. I'm just done with lenovo at this point. After they gimped the X280 I said that was the final straw.
I'm a bit miffed about the X280 design choices as well. It should have been an X280s, with the regular full-fat X280 still having all the good features, like a removable battery.
I hope they'll make an X280p or something that's more like the older X Thinkpads.
