-( 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. I would advise doing this as soon as possible, as the Blue Eco vents help out, so the sooner the better, as Blue Eco aids in the collection process.
Level: Precursor Basin
Near the mole hole up on a higher level, you should be able to see a floating purple Power Ring. You will need to drive through it to start the driving course to test your skill of speed through Precursor Basin. You will need to navigate through, I believe, twenty of them to net yourself a Power Cell. Thankfully, there aren't too many courses like this through the game (just this and the Blue Power Ring course also in Precursor Basin). Though you may not see a timer appear, you are timed, so try to get to the next ring as soon as you can.