My trolling motor has been acting up :'( it's a bow mount 54lb thrust motorguide. Bought it in November new at first it wasnt running strong, so i took the battery to wal-mart and it was bad so i bought a new one. When i was using the new one it worked AMAZING but after the first 2 trips it went bad. the batterys still good but the trolling motor goes bad after about ten minutes. but when i get home and plug it in it works fine, just in the water it doesnt. any idea?