GPS setup for use on the snowmobile (sled)

Sealed Lead Acid 12v / 1.3AH battery (weight 1.5 LBS - glad I'm not hiking with it).  The goal with this battery is to be able to go on a multi-day snowmobile trip and not have to think about recharging it - and to have it have enough juice to power the GPS under cold temps.  It's also nice not being tethered to the sled if I ran off of a sled power supply (it does not have 12Vdc)
Garmin GPS III+
42" RG174 antenna extension (RG58 was too rigid and the connection would pull out of the antenna)
Some hook-and-loop fasteners

42" RG 174

Battery in top pocket - GPS in lower pocket