need a battery for a trolling motor only project, motor is a 55 lb endura max , wot is 50 amps ..looking at batteries and some have the reserve minutes some just have the amp hours...im thinking reserve minutes is the best to go ..so say a battery with 200 reserve minutes divided by 50 amps= 4 hours of running at full speed???/ right? just dont want to paddle ...am i on the right track...so far i found a duracell ultra for 99. bucks it has 225 reserve minutes ..