I'd think your battery life would remain much the same. If you want better battery life you'll see more variation between kernels than DE's, in my experience.
You might get better battery life with a less demanding DE such as xfce, but overall the DE doesn't make much difference, at least in my experience.
You should give powertop a try if you want to extend your battery life.
The wireless should be much the same. You may get better support for your wireless card in mint by using mintwifi and attempting to install the proprietary windows driver.