Does battle ranking determine how much CP you get at the end of battle? I used to get max stars but now x.x I sometimes get 0. Gran pulse monsters have too much HP.
Your battle rating does indeed determine how much CP you get. If you've made it to Gran Pulse, right as soon as you enter the area to the right is a Behemoth (once you come out of the crevice and passed the save point). This is the first part that is an easy CP farm. The trick is to PS him and kill him before he unstaggers. It's like 8000 CP each time if you 5-star it (which you will if you PS him). Once you kill him just run back to the save point and he should respawn. After power-leveling your characters a bit and depending how much grinding you did before you got here, you should be able to beat him in 6ish seconds if not less (with a PS).