(spoilers, and partly replying to your earlier comment above): It's shown here because part of the storyline requires getting a car. The story specifically has him with a car available, but no battery which he has trouble getting. Just before this scene, he is told there is a car he can use, but of course he opens the bonnet and there is no battery installed (or, it's just the case, I can't remember).

As to why the lid should be in the fridge? My real-world guess is so all the bits are in one place, but the real reason is likely because the audience will more easily recognize the top of a battery over just seeing the chemicals.

The lid was so they can concisely communicate to the average viewer that we're looking at components for a battery.

The top of the case is right there. The rest of it is just a plastic container and doesn't need to be in a fridge.

I pulled this image from a random blog about the episode. The episode itself has better shots of the components