-( 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: Sentinel Beach
While running through the beach, you may see a Power Cell just lying out there on its own. A pelican will fly by and scoop it up, landing on its nest out in the water. Swim over to it and knock it, then rush to where it is. Thankfully, you could use the little water wheel directly across from the island, then punch-dash over to it to snag yourself the cell and this trophy.