we have a 4 stroke 10hp aux motor so we always have a way to get home, the battery never gets low enough that it wont start the motor but sometimes its low so the motor only just cranks, what i wanted was a way of telling when that point was close so we could start it to recharge the battery, the 4 stroke aux motor is a pull start one so dosnt need a battery. i am now thinking of monitoring how much we are drawing from the battery and doing it on a time based method so say deducting how many hours we have used say 4 amps from the overall amp hour rating, not accurate i know but maybe a starting place, and monitoring how many amps we are drawing will lets us know when we get a short, sometimes when salt water gets into something we find its shorting the battery out. the battery is replaced every year BTW