the more features the FF/DF has, like gps/2d/di/si, the more power hungry they get. Get a Low HDS 5 with SS/DS or similar HB, and you'll need something other than 8 AA batteries for a day of fishing. Lots of yakers use deer feeder batteries in a plastic watertight box to power their FF, these will last usually 2 or 3 trips or more before needing to be charged up. Just a gps/2d FF will last all day on the AA battery pack. I have a Low Elite 5 pro on my yak, and with a standard deer feeder battery, I could go 3 or 4 trips (18-24 hrs) before I would even consider charging the battery. I'm upgrading to a Low Elite 4 gps/ff because I wanted to reduce the clutter and eliminate the HH gps I carried.
Mounting one is not difficult, both Low and HB have quick disconnect mounting brackets, or use a ram mount, check out the small boat/yak forum, there are some threads on mounting FF and powering them up.
GO BIG ORANGE !
I meant to behave, but there were just way too many other options available at the time.