So we all know to ditch the wing nuts on start and house batteries and go with proper SS nuts and lock washers, right? On most batteries I've seen, the posta are different sizes to lessen the chance of connecting reverse polarity.
My suggestion is to head to local pawn shop/flea market and pay one or two dollars for a double-ended wrench with 1/2" and 9/16" openings, or whatever size your particular battery needs. Wrap the handle in bright coloured electrical tape for visibility and jam it into a battery box or somewhere handy so it's always available to remove a battery without rooting around in the regular tool kit.