I have a marine deep cycle kept on a charger for power outages and hurricanes. The top of the battery has standard car posts, but also 5/16 threaded studs. That made it easy to attach the charger and other electronics.
I wanted a wrench that would always be close by incase I needed to disconnect something or reconfigure it. Being plastic it meant I couldn't accidentally short anything. I made it short to get into the tight spaces of my battery storage box. A small bracket keeps the wrench safely stored close at hand for when it is needed. Wrench is for a 5/16 nut, it is not a 5/16 wrench.