cant figure it out

[Strike_King 609]

i bought 3 new batterys 2 trolling and a starter i also bought a XPS 3 bank 15 amp charger. I fished for 4 days without having to charge it. I plugged it in thrusday night. I checked it before we left today and the XPS said go fish meaning that it was fully chargered. I get to the lake turn on the bow mount trolling motor an it tells me that its fair not good. it lasted for about 2 hours but really had no power. Its a 75lbs thrust my question is did i hook it up wrong i know that i had to connect the battery backwards to get the 24volt trolling motor to work. However i didnt hook the battery charger up that way it has 3 plugs so i just hooked the post to the neg on all 3. Am i suppose to hook it up the same way i hooked the trolling motor up? this is 2 time this has happen everything is less then a month old i have only been out about 10 times. thanks for any advice