-( Story related, cannot be missed )-
*While this is "flagged" as possibly story related, the real note is that... you could scrape by without having all 101 Power Cells early on. It would be in your best interest to avoid back-tracking at the end to get this for the final ending.
Level: Boggy Swamp
While running around the swamp, you will come across a trashy citizen of the swamp needing your help to get his pet back. He has set out the pet's favorite treats and wants you to keep the swamp rats away. You'll be set up over a Yellow Eco vent and put into first-person view. The goal is to keep the rats away from the weird treats. It would do you well to spam-shot the pests away, though you will need to aim more carefully. In this view, none of your shots auto-path to the target (unlike if you were in third-person and shooting with Yellow Eco). The amount of rats and their A.I. will increase with each round, but after some close calls, you will find Farthy returning to his owner and a Power Cell will be yours.