Why is it bad to use a trooling battery to start??

[drewmitch44]

Why is it bad to use a trooling battery to start an outboard? Just curious as i've been starting my 115 yamaha with a deep cycle battery for a long time now.

 

[JB]

Re: Why is it bad to use a trooling battery to start??

It really does no harm, Drew. Deep cycle batteries have a higher internal impedance than "starting" batteries and can't supply as much current, but they can usually supply enough to start an outboard.

I wouldn't want to use one to try to start a big I/O engine.

 

[drewmitch44]

Re: Why is it bad to use a trooling battery to start??

ok cool. thanks JB. I thought that it had something to do with the way an outboard charged the battery. As in the difference between how a starting and a deep cycle battery charged. Im about to switch to using a starting battery that is smaller than the deep cycle that i was using and moving the deep cycle up to the front to run all the electronics. Im not sure how to charge both batteries so im going to have 2 deep cycle batteries under the dash to run all my accessories that i will take out of the boat after each use and charge with a plug in type charger. Thanks again!

 

[Chris1956]

Re: Why is it bad to use a trooling battery to start??

Drew, I have heard that the starting battery has harder plates than the deep cycle batteries. The reason was that harder plates were more suitable for supplying the large amount of current needed to start the motor.

They do have Marine Starting-Deep Cycle batteries. I used one for some years. it didn't cost any more or last any shorted than a plain starting battery. I will guess the plates are half-hard.

 

[QuadManiac]

Re: Why is it bad to use a trooling battery to start??

Using a trolling battery for high current starting applications will reduce the battery's expected lifetime. I wouldn't worry about it too much, though. However, you will not be happy if your trolling battery refuses to turn your starter when you're 5 miles out from the dock.

 

[Scaaty]

Re: Why is it bad to use a trooling battery to start??

Deep Cycle batts have thicker plates, so less plate area. Don't ask me why a Deep cycle works as it does, compared to a starting batt (just Google for a full explain)
That said, I bought a Deep Cycle 8 years ago from Cost-co. In my 88 125hp bayliner....did I say 8 years ago? I just float charge (cheap Harbor Frieght) over the winter. Zero problem (and JB right here too..not for the big V-8's)

 

[Texasmark]

Re: Why is it bad to use a trooling battery to start??

Thick plates not only tolerate vibration damage better, but apparently tolerate repeated deep cycling without damage better and that's why they are used.

Like stated in a couple of answers, deep cycles have thick plates so you can fit fewer in the given battery dimensions, hence less surface area in contact with the solution and consequently less peak current capability.....More impedance as JB said.

A trolling motor may run 40 amps for a big motor on full speed, whereas starting a large engine can whack 200 easily...there's the difference.

But a few years ago, I bought a 300 cubic inch diesel engined farm tractor that had a single battery for starting and it had obviously been there doing it's job and then some, for a very long time. It was a deep cycle, not combination start/cycle.

I was amazed. So I guess you never know.

Mark