Boating: #1, #2 or both?

[Matthawkins]

I am not clear on the proper way to run an outboard with two batteries and a switch. I have been given contradictory advice by the mechanic and the rep. So what do you know? When should you use a single battery and when shoud you use both? I ask because we had an extremely irritating weekend of battery failures.

[Slamdance]

The way I've always done it is to switch to both batteries most of the time for starting and while running, and then switch to one (#2) when you are drifting and using accessories. That way you always have one strong battery to start the engine with even if you drain the #2 battery with the accessories. I think the alternator charges #1 first and then #2 only after #1 is charged. I could be wrong about that, but that's the way I do it and I haven't had any problems. Oh, then make sure you isolate them both (switch to all off) when the boat is not in use, like when it's on the mooring or the trailer.

[jmd]

I have a 175 Yamaha with the same set up as you're talking about. Typically I only use one battery at a time. I've always been of the opinion that an outboard doesn't have the power in it's charging system to handle trying to charge two batteries at the same time. Trying to do so could cause damag. I'll alternate using each battery each time I use the boat and leave it at the mooring on the battery that I feel has the best charge. (Usually just a guess) Since I was neglectful and failed to take both batteries out of the boat last winter and haven't had a problem with them in the past two years I feel pretty confident about my approach.

Good Luck

[Matthawkins]

I just checked with Perko regarding this question. Their response was thus: If you are set on "one" you will be using and charging battery one. If you are set to "two", you will be using and charging battery two. If it is set to All, you are using and charging both batteries. It will split the amp from the charger by two. When set to off no current is coming or going to the batteries.

They made no reccomendation as to when to run on single or dual batteries. I'm still confused.

[craigh]

There are two contradicting objectives here. Battery life and making sure you have a good charge to start the engine with. The theory goes: a battery that is always completely discharge will only last for 100 or so rechargings before it will no longer hold a proper charge. A battery that is only ever discharge say 5% will last for several thousand re-charging. The life of a battery is exponetially proportional to the amount it is discharged. If battery life is important to you, you should always keep your switch on all. If both batteries are on, each battery will share the load therefore only discharge half as much. As apposed to starting on one battery and putting the whole load on it. The other half of this story is trying to ensure that you don't completely kill both batteries and not be able to start your engines. This is where switching to one battery while your out on the fishing grounds has gained popularity. Bottom line is you need to determine what is more important to you. I always keep my switch on all. As long as you keep your batteries in good shape you shouldn't have a problem. But then again....

[Matthawkins]

More from Perko- they claim it is safe to to change the position of the switch while the engine is running from 1 to 2, 2 to 1, or all to 1 or 2. They say the swich is a "make before break" switch so it will make the connection to the new position before disconecting from the old position. However, it is not safe to switch from any position to off while the motor is running. this could damage the alternator unless the switch has an "alternator field disconnect" but I don't know why you would do that any way.

[jeffg]

Not to confuse the matter more, but you can always put a Starting battery in position 1 and a deep cycle in 2. Then you have a battery with the amps to start the engine and just use the deep cycle for drifting and running all electronics. That way each battery is doing what it is optimally designed for and should extend its life accordingly. Just switch to "all" on the way home to charge both.

Jeff

[mdglaw]

my memory from the time I had a sailboat with a battery switch that to some extent it depended on the nature of the switch. If they isolated the batteries they would operate to charge both batteries, and more important to protect the higher battery from discharging to the lower battery if left on both. If you do not have this isolation feature you don't want to run both batteries at the same time.
On my present 18 footer I run two batteries, a starting battery and a deep cycle for the trolling motor. I run the alternater only to the starting battery. It will not charge the deep cycle. You should be aware that gel cels do not charge at the same voltage as lead acid, this can be a problem with both alternator and charger. I have never run the deep cycle out, and then I have a very good double charger at home. I have saturated glass mat batteries that charge at a different voltage from the gels or traditional lead acid. My on board charger then goes from full charge to shutting off so there is no over charge.
Mike