Help!

Earlier this summer, I believe I didn't turn the key completely to off and left the lights on on the mower. I was able to jump the battery for each subsequent use off my truck, no problem. I finally got annoyed having to hook up the jumper cables and bought a new battery.

Installation is super easy and I had it done in minutes. One problem: it still won't start (no power, no click, nothing). However, if I simply put the cables on my truck battery, then the lawn mower, it starts, without me even needing to start my truck for power. I have noticed that when I put the second cable on the mower battery, I hear a very soft click. Then I just sit down, turn the key and it turns over/starts.

What in the world do you think the problem might be? It's a brand new battery.