Dual Batteries or Not?

[mklearl]

I've got my boat finally running soundly (for now) and have it pimped out with accessories. There is already a dual battery switch installed. I have read different opinions on dual batteries and am looking for some advice. The seloc manual for my 1979 chrysler 700 skier 70 hp says that the engine should be able to sufficiently charge the battery after starting and using electronics on board. However, electronics have come a long way since 1979! I have an aerator, bilge pump, running lights, horn, stereo, chart plotter, and fishfinder. My concern is that if I use all of these on the same battery, with the engine off (listening to the radio and using the live well while fishing) the battery will drain and I will be dead in the water. Any opinions on this before I do a "trial by error?"

If I do install the second battery, I would have one as just a starting battery and one to run the electronics. Doing some research, I have seen that the engine may or may not be able to charge both batteries. I'm thinking it probably will not. Therefore, what would I put the battery switch to? Keep it on the starting battery and just drain the battery on the electronics down until I get it home and on the charger? I know I could start it and switch the battery switch over to the electronics battery to charge, but I think I also read that this isn't recommended.

Thanks in advance

 

[wrench 3]

Re: Dual Batteries or Not?

Normally you have the switch on both when the engine is running to charge both batteries. But if your worried about overloading your charging system, you could leave the switch on the starting battery position for the run home, when the second battery is low on charge. Then re-charge it at home.
BTW the auxiliary battery should be a deep cycle.

 

[Georgesalmon]

Re: Dual Batteries or Not?

I start my engine on position 1 and then switch to both when running. If I stop the main engine I switch to position 2 and then I always have a fresh starting battery. Yes, I recommend having two batteries on the boat. My second battery is a combo start/deep cycle. You engine can charge both batteries from your engine if you run it long enough, but most people don't run their engine the amount of hours it would take to do that. I also have an onboard two battery charger that I plug in whenever I'm not using the boat. You can't "overload" your charging system it will only put out the max amps of what it can produce and that only if the batteries are discharged.

 

[Frank Acampora]

Re: Dual Batteries or Not?

Yes, definitely use two batteries if you have the room and the extra weight will not hurt. If you use the radio and electronics a lot, you do run the risk of not having enough power to start the engine. COUPLED with that is the fact that your ignition system needs power from the battery. If voltage at the battery is too low, you would not even be able to pull start the engine.

As said above, you can not hurt the charging system by charging both batteries at once. HOWEVER: If the second battery is really low, the primary starting battery will tend to discharge into the low battery until both are at equal potential. Thus, on the ride home, after starting the engine, I would use position two and only charge the discharged battery.

 

[mklearl]

Re: Dual Batteries or Not?

Great. Thanks. I thought I read somewhere that when the engine is running it is not recommended to switch the from one battery to the other because it can damage the charging system.

 

[Big Fish Billy]

Re: Dual Batteries or Not?

Or, start with both batteries charged fully from home. Have your switch on "1" when you leave the dock. Do all your running around and see if the 1 battery will do the job, running boat and toys. (which I think it will) Then just switch to "2" if you need the help to get back home. If you do need "2" to start the engine, once it's running, put your switch on Both for the ride. Then top them off again when you're home if necessary. No damage switching among the on positions, just don't turn it off while the engine is running.

 

[Frank Acampora]

Re: Dual Batteries or Not?

If you switch while the engine is idling, the alternator is delivering minimal amps and the switching is only momentary---no damage. I would not do it at full throttle though.

 

[mklearl]

Re: Dual Batteries or Not?

Great info everyone. Thank you!

 

[Big Fish Billy]

Re: Dual Batteries or Not?

If you switch while the engine is idling, the alternator is delivering minimal amps and the switching is only momentary---no damage. I would not do it at full throttle though.

Hopefully at full throttle people are holding on to the steering wheel and watching where they're going....but....you just never know....

 

[mklearl]

Re: Dual Batteries or Not?

One last question. I have a dual purpose battery in there now (starting and cycling). Do I want to get just a starting battery, deep cycle, or another dual purpose?

 

[Big Fish Billy]

Re: Dual Batteries or Not?

If you are going to use a trolling motor at all, I would use deep cycle, other wise dual purpose should be fine. One thing a lot of people don't realize is that you get about 220 cycles of discharging a battery from fully charged to below half charged on a deep cycle battery and about 30-40 on a regular battery if you're lucky....so use them wisely....

 

[oldboat1]

Re: Dual Batteries or Not?

I like the #6 suggestion. Use the starting battery for the motor and accessories to get a sense of what the draw is, knowing that you have the auxiliary battery to start the motor for the trip home. If after a day of using all the electronics, you will have a real world test of battery needs. I like a two battery system, and like big amp deep cycle batteries for both of them. Deep cycles seem to me to make good sense on boats, whether starting or auxiliary. They have a chance of standing up to storage, charging, discharging.... I have a couple of deep cycles on my 26' inboard cruiser, and have had no issues (had them put in last spring, after the starting battery died following winter storage). I also did dual deep cycles for a number of years on an outboard runabout and was very pleased (used a battery isolator on the runabout to charge both batteries simultaneously, and that worked OK. A switch is probably better.)