Peugeot 306 turbo Diesel engine

This picture I took a few days ago is when I was trying to disconnect the battery cables from my 306. The negative terminal came off easily, but the positive was rusted in. After a lot of work I finally disconnected the battery, however, I lack the tools to unscrew the battery holders. The battery I unscrews was completely dead and even broke the fuse of the battery charger when I turned on the ignition.