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Random Quote: Be sure your right, and then go ahead........
I know this sounds like a stupid question, but I just baought a new boat with 2 batteries and a switch. since all my others before this always only had 1 battery I thought I would ask for some input. when drifting with the electronics on, should I only have the switch on one battery or both. should I treat the 2 batteries as seperate or always use them in the "Both" position. I will only have a ff/gps and a VHF. maybe a cellphone through the cig. lighter. I also have 2 24v gel batteries for the Lencos that will be completely seperate with an on-board charger that I will power up from the dock. any input would be really appreciated
Regards
Brendan
1982 Mako 17' 2000 Johnson 115
2003 Steiger 21' Superfly 140 Johnson 4 stroke
I think most of us use one battery one time the other the next time. This way the other battery is a true back up.
However, if you do not have a built in charger while you are at the dock, beware that only the battery being used is being charged while underway. Do you have built in voltmeters for both batteries? They are worth having to give you a quick status of the batteries and to make sure your alternator is working.
Can you use the same charger that you use for the separate batteries for the dual engine batteries?
Bottom line is it depends on your charging and frequency of use. (e.g. if you do not charge the engine batteries at the dock you may want to charge both (one at a time) when underway by using one on the way out and one on the way back or some such system). But then you have to worry about restarting. I have heard it is not good to switch from one to both or to the other when underway ..
MC, I read that you have two 24v gels for the Lencos, I was going to install Lencos on my boat and was wondering if you neded seperate batteries for them. Unfortunatly I only have one battery on my boat and if this is the case, maybe I should be thinking about Bennetts..
Thanks in advance.
Al
Its not possible to answer that question properly because no one knows how your boat is wired. Basically there are two different ways (with a few variations) folks usually wire them.
One way is with each battery separately being able to handel all the boat's needs and you just switch between them on different days.
The other has two different type of batterys, one used for starting and one used for running the boat's system. With those setups you really have to look at specifically how its wired to make good use of it.
Everyone has their own preference for how to wire them, I go for the first method myself, and there are arguments to be made for each way. You have to figure out which way you want your boat wired, them make it so (an inexpensive thing to do and easy for a DIY project), and then use the battery switch accordingly.
Thom
"For every complex question, there's a simple answer. And it's wrong."
(--H. L. Mencken)
Thom hit the nail on the head. I had an 18' CC a few years ago, and had 2 identical batteries, and alternated between the two. You always run the risk of having 2 dead batteries by switching to both running running out to your destination, and then forgetting to switch back to 1 or 2.
I now have two different batteries - battery 1 is a starting battery, and battery 2 is a deep cycle.
While the boat is at the slip, it's on batt 2 (the house battery) and it keeps it charged up. This is a much bigger battery bank (more amp hours) to handle fridge, electronics, etc while anchored for a couple of days. It takes a while to charge it, so while at the slip, my switch is on batt2 to charge it up during the week.
Wehn I get to the slip for the weekend, I put it on batt 1 (starting batt) and start up the boat. I leave it on batt 1 the whole time I'm underway, which charges it back up. As soon as I drop the hook and I'm on battery power, I switch it back to batt2. I never put it on both, so I reduce the likelihood of managing to drain both batteries. I also don't put it on both for charging, since one half dead battery can pull down the other. I would only use both if both batts were half dead and I needed every bit of juice to start the engine.
In my old boat, which I trailered, I would leave it on both while charging, (ie underway) and switch to 1 or 2 while on battery power.
Never move the switch from "1" to "off" to "2" while the engine is running. It's a very convenient way to ruin a perfectly good alternator.
Going from 1 to both to 2 is generally ok as most switches are a 'make before break' connection.
Too bad your new boat manufaturer or dealer did not give you documentation or operation reccomendations for your battery switch.
But mine did not either. Nothing at all. No wiring diagram, no usage guidelines, no nothing!
The switch was...Just there. ONE-TWO-BOTH-OFF
Go figure how to add an inboard charger.
I've not seen a boat yet that had any kind of battery management system. This would be very high on my list of wishes as a retrofit and most important from the boat manufacturer. (Should not be rocket-science in the days of the computer. Sure would like to see a charge reminder, and a "push to test" button for assesing each batteries charge state and capacity.)
Basically, the way I see it today is that dual batteries in the back with a switch is about like having an expensive pair of jumper cables.
However, if you ever need the cables and/or the duals with the switch, you will be glad you have both.
As usual, you guys are awesome with your input. I have paid for this boat but they are storing it for me until spring since I live in Manhattan and have no room to keep it!!! . As far as the Lencos, they are the ones with the trolling motors on them so the boat is rigged with the 2 24 volt gel batteries and charger as a seperate system.as far as I know I cannot use the motor to re-charge these batteries since they are 24 volt.As far as lenco tabs I don't think you need seperate batteries to run just the tabs themselves as you are usually underway and the 12 volts are charging at the time anyway. the 12 volt batteries(also in the console)are set-up with the switch. so Thom's input is great as I think they are set-up to run everything on either battery. I used to have this on our sailboat growing up and always put it on both when runnuing motor and used i or the other when not running the motor. I will ask the manufacturer (Steigercraft) how it is set-up before I take delivery of the boat and thanks agian for all your input.
1982 Mako 17' 2000 Johnson 115
2003 Steiger 21' Superfly 140 Johnson 4 stroke
One other option is to run a battery combiner between the batteries, and leave the battery switch on either 1 or 2. The combiner senses when the engine is running or when a charger has been connected and activated by a rise in the voltage. The combiner then switches a relay to connect the two batteries in parallel, allowing both batteries to charge together. When the voltage drops below a specified point (around 13.2 or so), the switch opens, disconnecting the parallel circuit.
The advantage of this setup is you don't have to keep track of which switch position you last used to keep the charge up from the engine.
How do battery switches work??? 
