I have a 2008 and I just replaced both my batteries, I was told the way to tell if your batteries need replaced is to charge them to full then test them they should read 12.7-13 even though its only a 12v battery, then wait a couple weeks or so test them again, if they drop below 12 they are losing a charge. They are deep cycle RV/Marine batteries. I take mine out of my rv during the winter, they also told me to make sure they are fully charged when I store them, (disconnect from charger when stored) check them several months later if below 11 replace them, just a couple ideas.