There are no free lunch;s when it comes to Deep cycle batteries. Efficiencies and weight vary little across brands. Most 25-45# trolling motors are going to require the reserve of a size 24 or 27 battery. Try a smaller one and you'll be paddling back to the ramp at the end of the day. If you want to go to a smaller battery ( like a U1) you need to draw less power. Most major trolling motor companies do market variable speed motors with special circuitry that sip power at low to medium speeds ( that in turn MAY let you go to a smaller battery.)
FWIW, I can get 3.5-4 hrs run time on a 30# Motorguide Varimax at 20# thrust off a U1 battery. Cut that in half If I run near top end.
FWIW, I can get 3.5-4 hrs run time on a 30# Motorguide Varimax at 20# thrust off a U1 battery. Cut that in half If I run near top end.