Thread: two or more batterys in your boat

Too many unknowns. There are switches called "make before break" that make sure the second battery is connected to the outboard before the first is disconnected.

Many outboards don't have enough charging capacity to even consider trying this, and even with larger outboards with alternators it's only useful if you make long runs at high speeds so the alternator has time to do any charging.

Crappie fishermen tend to spend much more time fishing than running, so in many cases they can't even keep their outboard battery charged, let alone a TM battery too.

I can understand that will have to remember to make sure I have good charged batterys before I go out in the boat from now on..I will get a good deep cycle battery for the trolling motor. didnt realize that the motor only charged up a battery verry slowly.Thanks

The alternator only produces 12 to 14 volts, it produces that at idle and it produces that at high speed, it doesnt make any difference about engine speed while charging or I should say it shouldnt if everything is working properly and no it will not fully charge the battery. A battery charger produces say 30volts and it still takes a while to charge the battery at 12 volts it would take between 4 to 6 hrs to get close to a full charge.

Originally Posted by MorganT69

The alternator only produces 12 to 14 volts, it produces that at idle and it produces that at high speed, it doesnt make any difference about engine speed while charging or I should say it shouldnt if everything is working properly and no it will not fully charge the battery. A battery charger produces say 30volts and it still takes a while to charge the battery at 12 volts it would take between 4 to 6 hrs to get close to a full charge.

The above statement is not correct.
"Charge voltage" and "amps" are not the same. At idle, the charge voltage should be at or below 14.5v but the amp output will not be sufficient until high rpm is achieved. The big V6 engines only put out around 40amps max. Which would require several hours of high speed runs to charge a fully discharged battery of a size found in most boats. Most outboards have a smaller amp output rating and would require even longer run time.
A good automatic battery charger will not exceed 16v while in a desulfication mode.
The only chargers that I am aware of that reach voltages approaching 30v are the roll around shop style charger/jumper boxes. Most of them have a low/med/high setting that really crank out the voltage on high. If you were to charge a battery for any length of time at voltages near 30v., you can expect a strong sulfur odor to develop as the electrolyte is boiled out of the cells. Short battery life and the potential for an exploded battery should be expected.

Originally Posted by sliderman

The above statement is not correct.
"Charge voltage" and "amps" are not the same. At idle, the charge voltage should be at or below 14.5v but the amp output will not be sufficient until high rpm is achieved. The big V6 engines only put out around 40amps max. Which would require several hours of high speed runs to charge a fully discharged battery of a size found in most boats. Most outboards have a smaller amp output rating and would require even longer run time.
A good automatic battery charger will not exceed 16v while in a desulfication mode.
The only chargers that I am aware of that reach voltages approaching 30v are the roll around shop style charger/jumper boxes. Most of them have a low/med/high setting that really crank out the voltage on high. If you were to charge a battery for any length of time at voltages near 30v., you can expect a strong sulfur odor to develop as the electrolyte is boiled out of the cells. Short battery life and the potential for an exploded battery should be expected.

Yep