If you are using a traditional battery clamp where the bolt just tightens the clamp around the post, then the bolt has nothing to do with the situation other than holding the clamp together, noting that I would not recommend placing a galvanized bolt into the installation in such a way that current flows through it and it becomes apart of the circuit, not that it would not conduct current, but because of the issues that can result from the galvanization exposed to electrical charge this way. Batteries are consumable items to start with, as the battery ages the plates develop a scale that reduces their effectiveness and can come lose, becoming a sediment in the bottom of the cell. If this sediment becomes deep enough to contact the battery plates, then the batter develops a short and fails as a result. I have actually revived dead batteries by dropping an aspirin into each cell, which causes the scaling on the plates to shed and present "fresh" material to function as an active portion of the battery. After the aspirin treatment, the batteries need to be completely flushed and the sediment removed and new acid provided. If the plates are not too far gone the battery will work well after properly charging. If not the battery may be too far gone, internal connections dissolved etc and the battery is junk.
