Its about 8 years old, but a t460 with the beefier removable battery will easily hit 8 hours doing office work and browsing. You can squeak 12 out of it if you turn turbo boost off on the CPU.
I used to use this laptop daily. It's too slow for everyday use. YouTube videos lag if you're streaming at more than 720p or if you're doing anything else, including outputting to another monitor.
I can't recommend a dual core CPU unless you're sure you don't need to use anything more than that.
I can't recommend a dual core CPU unless you're sure you don't need to use anything more than that.