ThinkPad

Depends on what you're doing with the machine really. Full blast load will be about the same battery life since it will be limited by the 35 watt TDP (assuming you get a sane CPU). But idle and low to mid loads expect 1-3 watts more usage any any given time.

It's been a long ass time since I looked into it, but dual core vs quad core in my sandy bridge T420 got me like 6 vs 7 hours of battery life. But that was also like 10 years ago and the internet is far more intensive these days so I'd expect a much bigger hit.