If you are looking for a GPS unit that has a considerable battery life, then the first thing you want to check is what type of battery the unit you are interested in has installed. If the GPS unit takes AA batteries, then don’t bet on the device giving your more the 8 or maybe 9 ours of continuous operation, max.
Lithium ion batteries on the other hand not only last more than five times that much, but they have the added bonus of being rechargeable. So if you are going to be out on the boat every weekend, then the extra price of a more advanced GPS fishfinder might just be worth it when you think of how much you will save on batteries.
As far as the GPS units on this list are concerned, the Garmin GPSMAP 86s has the best battery life, clocking in right around 50 hours.