Attach a 13mm socket to a ratchet extension then attach the extension to a drive ratchet.

Loosen the 13mm bolt from the negative terminal of the battery.

You do not need to remove the nut from the terminal bolt completely. The terminal should slide off the post once the nut is loose.

Be sure to keep your ratchet or any other metal items from touching both the positive and negative terminals while performing this task. Connecting metal to both terminals creates a new path of electricity and could cause serious chemical, electrical, and flammable damage to your equipment and/or health.