Questions about T480 Battery, few other things

I'm planning to purchase a used T480, and want to know how the battery life would be on Linux. Online I see a lot of good numbers, and I am considering carrying multiple of the external batteries, but I want another opinion. Also, do you have any recommends on a good price to "go for it" and any other laptops to consider (up to but preferably well under 600 USD, good battery/portability, linux) to consider.