How many hours should a battery on a boat last and how do you tell if it is low or dead?

On most boats there are two batteries- a trolling motor battery and a cranking battery. The cranking battery will last several years is it is kept charged up- you will tell if it is low of charge if it slowly turns the motor, or does not turn over at all .

The trolling motor battery is quite different- on my fishing boat I have tried most major brands of trolling motors- none have lasted me over 24 months, regardless of the price I paid for it- you will notice the trolling motor batteries have only a 12 month free replacement warranty on them- my batteries usually last14 to 15 months- I believe that it has something to do with the amount of times you run them completely down and recharge them- there is only so many cycles that they will take without going bad- You can tell when it is time to replace one when it will run down after an hour or two of use, or when the charger can't charge it enough to kick the charger off, by never reaching the full charge required to kick the automatic charger off.

If you are using the battery to power a trolling motor, and have a deep Cycle 105Amp battery, on 12 Volts it should last about 4 hours. A volt meter will tell you when it's too discharged to continue. Then recharge it, and so again. These battery's usually last about two seasons, not because of too much use, but too little. It's lack of use that's hard on them. I rigged my battery as an extra(2nd) battery on my Dodge van. It recharged with normal use and lasted five years. When I got to the ramp, I opened the battery compartment and took the battery out and put it in the boat. I never had any problems with it.

What is your use? Trolling motor? Starting battery? Cranking tunes?

Is the battery a deep cycle or just a cranking battery?

On my fishing boat running the trolling motor at 30% power, one deep cycle battery will last four or five hours. At full power it won't last an hour and a half.

Cranking tunes on my ski boat battery which is dual purpose will kill the battery in about two hours.

If you are talking about how long a starting battery will provide service: I live in a very cold climate, and it is hard on batteries. If you really treat your battery right five seasons is a fair service life.

Hope this helps.