I'm upgrading some batteries in my boats. Both are 12 volt systems but one has factory connections for two deep cycle batteries. I plan to put the deep cycle battery that's in my bigger boat into my smaller up north boat. I then plan to get two new batteries for my bigger boat that has the two sets of cables. I've been told to get a "matched set" of batteries. What does that mean? Bought on the same day? Same manufacture year/month? Consecutive serial numbers? Thanks for your help.