Battery question

[r8rfan]

Have a 1982 mercury 40 horse. Has the thunderbolt ignition. Does it charge the battery while running? I just bought the boat and the trolling motor is hooked to the same battery as the outboard. I'm wondering if I should buy a battery for the trolling motor or will the mercury keep the battery charged as I change fishing locations periodically? I'm guessing I should just buy a battery, but if the mercury is capable of keeping the battery charged then I'll leave it well enough alone.<br />Thanks a lot.

 

[DJ]

Re: Battery question

r8rfan,<br /><br />I'm not sure if your Merc. has an alternator system. However, it's easy to check. Buy a cheap multi meter and check the voltage with the engine running at cruising speeds. If it's over 12.5 volts, you're good to go.

 

[neumanns]

Re: Battery question

Regardless if you have an alternator buy a deep cycle trolling motor battery. the charger on the motor is designed to keep the starting battery up only. Or you can use one battery and when you get ready to change fishing spots find you do not have enoufgh battery to crank your engine then you could procede to paddle back to the ramp.

 

[farginicehole]

Re: Battery question

I was told once by a battery expert(?) that you don't want to use a deep cycle battery for a cranking application. Can't remember exactly what his reasoning behind this was, but it seemed to make sense at the time. Maybe someone here that knows can comment on this? I would still go with a cranking battery for starting your motor and a separate deep cycle for your trolling motor. Would also highly recommend a good onboard charger, such as a Guest. They're a little expensive, but I think they more than pay for themselves with the great condition they keep your batteries in and you can also leave them plugged in indefinitely. I'm going on about 4 seasons now with my cranking battery and my two deep cycles! I'm not a tournament fisherman, but I still use them quite often.

 

[petryshyn]

Re: Battery question

Deep cycles can be used for cranking. The only concern is that they are sized correctly for the job...

 

[Boatist]

Re: Battery question

Any Deepcycle battery with enough amps to run a trolling motor will have enough Amps to start a 40hp motor. Still not a bad idea to have two batteries to make sure have enough charge to start your 40 hp motor at the end of day.

 

[bountyhunter39]

Re: Battery question

Wont a deep cycle burn up your stator?

 

[rickdb1boat]

Re: Battery question

Some good reading on Batteries<br /><br /> web page

 

[FlyBoyMark]

Re: Battery question

Deep cycle batteries are fine for cranking...the problem arises if you you have to grind the starter for a continues period of time to clear a flooded engine as an example. Deep cycle batteries are designed for lower continues amp draw and not 100 or more amps continues. Deep cycle trolling batteries are based on a 25 amp draw rating and cold cranking you will see on SOME of them is a bit less than a standard cranking battery of the same size. They will tend to go slightly flat with low voltage till they have a chance to "catch up". Low voltage is the enemy to your starter. On outboards of 60 HP or less this is nill factor because thier starters usually only draw 50 to 80 amps. If weight is a problem, you can use a lawn tractor size battery(they make them for marine use too...) for your starter and Deep cycle as a backup with a switch. They have more than sufficient power for 20 minuts of cranking even on the biggest outboards.

 

[John Reynolds]

Re: Battery question

FlyBoyMark has got it right on the mark

 

[Boatist]

Re: Battery question

Bountyhunter<br />You make a good point there. Not really a question of a deep cycle battery burning up your stator. More a question of a discharged battery burning up your stator. For me if I was running a trolling motor I would use two batteries, one for starting and one for trolling motor. I would use a battery isolator and limit current to trolling motor to 1/2 half of my stator/alternator output. This way your starting battery charges up fast and then your stator will drop to about half of it max output to put some juice in the trolling battery. Bottom line if he run 5 minutes acrossed the lake and fishes for 2 hours with the trolling motor then run 15 minutes to another spot, the trolling motor is not going to get much charge. May get him a few more minutes on the trolling motor. If he had a big motor with a 40 amp belt driven anternator then could actually do him some good.

 

[DJ]

Re: Battery question

Deep cycle batteries have more plates than a typical cranking battery. Because there are more plates, they are closer together.<br /><br />Heat is the enemy of any battery. Because the plates on a deep cycle are so close together, one stands the risk of warping them and shorting out the battery. Warpage happens when a great deal of amperage is needed for extended periods. Such as cranking an outboard for a long period.<br /><br />If your big outbaord starts VERY easily, the deep cycle probably wouldn't get hurt, however, one time having to crank alot may kill the deep cycle.

 

[Boatist]

Re: Battery question

R8rfan<br />I am not sure if your motor has a battery charger or not. Like Djohns says if over 12.6 volts and riseing while you are running then it does.<br /><br />Small electric start motors in the 80's usually did have some sort of charger. In general only 6 to 10 amps. So if you ran your trolling motor (40 amps or more) for an hour it would take 4 hours at 10 amps to recharge. This would be very hard on your charger circuits. So I would reccomend you get a seperate Deep cycle battery for your trolling motor and charge it as soon as you get home.

 

[Boatist]

Re: Battery question

DJohns<br />I have to disagree, Deep cycle batteries have fewer thicker plates. For that reason may not be able to supply as much current for starting, but he has a 40HP motor. Starter on that 40hp may not need as much current as his trolling motor on HI.