This is probably a dumb question if it is I apologize in advance but here goes. When I plug my Ranger 3 bank charger in to charge my batteries the bank that charges my cranking battery will go green in about a couple of minutes. But after about 5-10 mins it will go all red and no matter how long you charge it will stay all red. The other 2 banks that charge my trolling batteries will work as expected. They start out red but after several hours will go green and stay green. The only thing I could think of is the bank that charges my cranking battery is bad but I don't know how to check it. Any ideas? Thanks for your help.