Something I've done to solve my GPS power issues:
For a sled that doesn't have a battery, the power will only be provided when the motor is running. Turn off the sled, and the GPS dies (alkaline batteries suck in the cold, and won't last me a full day with this setup). So, what I've done is taken a battery from an R/C car and fabbed a harness to it that I can use the aux power port on my GPS just like it's plugging into the sled. Now, I have power regardless of sled status, and I store the battery under the hood so it stays warm and lasts many days without recharging. Plus, an added benefit, in the event I have to leave my sled I will still have a solid power source for my GPS as I can take the battery pack with me (it's about half the size of a deck of cards and weighs very little).
Works great for me....