The Thinkpad T4x0 series has two batteries as well. I had a T450s at my previous job and I think I'd get 6-7 hours out of it (usual workload of ssh, vim, 50-100 chrome tabs, slack, google play music all running).
I wrote about my experiences with installing Linux on it here: https://medium.com/@debugjois/installing-ubuntu-gnome-17-04-... (it’s a bit outdated. I run Arch on it now)
The only thing that Arch clearly improved was the Bluetooth experience, which was very unstable on Ubuntu (even after the upgrage to 17.10). But even that is probably down to the newer kernel in Arch.