I have been looking at sears web site and they list 3 deep cycle batteries. 24m,27,29m. question is example 29m specs- 200 minute reserve- 115 amp hr at20 hour rate. what does that mean, how long can I expect battery to operate trolling motor. others, 27m- 180 reserve-105 hr at 20 hour rate. 24m- 135 reserve-80 hr at 20 hr rate. I know it has to do with time it will stay charged but not sure how to figure it. help please??