How long your battery will last depends on a lot of factors, 2 of the biggest are..........
1. The more thrust it puts out the greater the power drain.
2. The quality of your battery and how many cold cranking amps it has.(a 500 amp battery will not last as long as a 700 amp.)
As for a stern mount vs a bow mount. I have found when battling winds like at Aurora I have better boat control with the bow mount. I am pulling the boat rather than pushing it. With the stern mount, going into the wind the bow acts like a sail and will get pushed to the side requiring a lot more correction. You end up doing a lot more zig zagging, and since there are very few submarines looking to sink a fishing boat in Colorado a Straighter course is better unless you are deliberately zig zagging (like during a troll)
On thing that a lot of people forget is you need a longer shaft for bow mounting than you do for stern mounting.