i have a minnkota ulterra 24 volt 80 pound thrust trolling motor on 2021 g3 sportsman 18ft boat. im assuming it still has the original batteries. they are tied together to get 24 volts and charged onboard . i have noticed on my trolling motor remote, the battery signal showing half charge after a little running as of late. at first i thought it was the battery to the remote but that turned out to not be the case after i replaced those triple a batteries. So noe im assuming that means i probably have one battery starting to go? it has always been plenty for my trips, but dont want to mess around when i can just go buy another battery. so my question? how can i tell which battery is bad? and would the battery i replace it with need to be the same brand(obviously it would be 12volt and similar cca)?