Currently running an minn kota ulterra with 4 group 27 interstate batteries. I do a lot of trolling. Two batteries would not last but about six hours. The four batteries fixed my problem . Just installed a new ultrex on the boat. My batteries are six years old and will be replacing them shortly. Was thinking about trying to go with two group 31 interstate . I know lithium is what a lot of people are using but I don't care for the prices they charge. Anyone trolling with 2 batteries (old style) and have enough juice to run 8-10 hours especially on windy conditions with an ulterra. I know I can go right back to the four group 27 batteries like I have now for 600 bucks cost. Trying to save some space and weight in my boat. I have been told the onboard charger I'm using will not work for lithium. It is an older model guest charger