The battery for a D5300 is the EN-EL14(a). It comes with a piece of moulded plastic which clips over one end of the battery to protect the terminals. It doesn't offer much protection for the rest of the battery, and it's easy to lose.
An alternative can be found with a Tic-Tac box. For this particular battery, the right fit can be found with the 29g (1oz) size of mints.
The lid of the container is exactly the right size for a 'push-on' fit over the battery terminals. I superglued the flip-top of the container shut to help with water-resistance.
A bit of foam at the bottom of the container helps in case the battery dislodges from the cap.
That's it. A bit of added protection for a quite expensive battery when we're out trekking across the wastes of Essex.