I replaced mine a few months ago, it was a pain.. Would like to speak with person that came up with that design, they could have simply made the access cover larger for battery replacement.
Along with a few plastic fender clips, you will need to remove the 2 tie down rings, pop off the covers and remove the screw beneath the covers, then the rear/back plastic piece can be removed, in order to remove the side panel. Loosen/disconnect the negative side terminal, then Carefully open the plastic cover on the positive side (mine broke), loosen/disconnect, then remove hold down brackets.