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305 battery config.

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    305 battery config.

    So I have a new to 2005 305 - very happy with her. I have a two battery set up with two 350 mags. The batteries are in parallel - what s the config for the swicthes - manual says do not run the engine when the two battery switches are on, Should it be engines on ONE and house on TWO? Help please.



    It should read not to run the engines with the battery switches turned off.
    Rick Grew

    1981 Carver 3007 Aft Cabin

    2004 Past Commodore
    West River Yacht & Cruising Club


      One more thing never switch, battery switches when engine is running, it will blow the diodes in the alternator , now some switches are protected but why take a chance. Protected switches are marked.
      Slightly modified 2859 6.5 Diesel Bravo III X drive
      96 Dodge 5.9 5 speed Gear vender OD.


        For some reason, similar boats are often wired differently. Generally, one battery should be starting and one house but it isn't always the case. Only way to know is to follow the wiring. As previously stated, the manual is in correct.
        Hanging Loose
        98 Carver 350 Mariner
        2001 305
        5.7 BII


          Peter - Your (and others) confusion is understandable. I realize this is an old post - but if you're still uncertain, perhaps this will help.

          I'm guessing your battery switches look like the ones in the picture - that's how they came from the factory (the photo is a 2006 boat but they didn't change much if at all going all the way back to the 3055's in the late '90's.

          So - Problem 1: 99% of the 3055/305's (even those equipped with a genset) were delivered with just TWO batteries, unless the selling dealer added more. A twin-engine cruiser should - and most do - have at least THREE batteries (or battery "banks", if you prefer) - one start battery for each engine, and a separate, deep-cycle, HOUSE battery. That is not how Bayliner designed or built their cruisers. So unless your boat had additional batteries added by someone, which it may well have, then you're working with just two batteries.

          Problem 2: If you look at the labels for the two battery switches, you'll be even more confused. That's because one of them is labeled ENGINE (singular, not plural), and the other is labeled HOUSE. Huh? Clearly, you have TWO "Engine(s)", so WHICH engine is that upper switch referring to? Or does it refer to both engines? And as I've already explained, you most likely don't even HAVE a dedicated House battery, so.... how can one switch be labeled "House"?

          If you take the time to crawl up behind the battery switch panel (in the engine room) with a flashlight and your camera, you'll probably find essentially what I have sketched out in the PDF attachment. I say "probably", because this entire post should be prefaced with the standard disclaimer that the ONLY way to 100% confirm how your particular boat is wired (including a NEW boat), is to inspect the system and confirm it with your own eyes - there are unlimited possibilities for previous changes that may have been made to the system before you got it. That said, here's the summary of the way it was designed:

          You have two, identical Group 27 start batteries. They ought to be referred to as "1" and "2", and this is how the switch is labeled. Battery "1" is connected to the "1" terminal of both switches, as shown. Battery "2" is connected to the "2" terminal on both switches. So, when you select the "1" position - with either switch - then you are connecting the load for THAT switch to the #1 Battery. Same with selecting the "2" position on either switch - you are connecting the load for THAT switch, to the #2 Battery. OK so far?

          Now the question is - just what ARE the loads connected to those switches?

          The upper one is labeled "ENGINE" - in fact, it is connected ONLY to the PORT engine, and also the Genset starter if installed. So, the first thing you probably ought to do is get your label maker out, and change that label to read "PORT ENGINE", or "PORT ENGINE/GENSET" (if your boat has the genset option). Then, things start to make sense. Selecting "1" with that switch, connects your Port engine to the #1 battery, selecting "2" connects it to the #2 battery. Simple enough, right?

          The lower switch, you might guess, is connected to the STARBOARD engine - and you'd be right. However, it is ALSO connected to pretty much ALL of your "House" loads - that's why they labeled it HOUSE. You will see a fairly good-sized conductor, perhaps 4AWG, that goes directly from the common terminal on that lower switch, to the 50A, push-pull circuit breaker labeled "Accessory". This is actually the DC Main feed that goes to your helm area and feeds virtually every circuit on the boat, not related to the engines. So - grab the label maker and rename this switch "STARBOARD ENGINE/HOUSE". Got it?

          If you study the somewhat confusing table that Bayliner has included on Page 60 of the Owners Manual Supplement (attached), you'll realize that it confirms which loads are attached to which switch, though it's not very well explained, IMHO.

          Now stand back and think about it. Obviously, it makes sense to connect each engine to it's own battery, but does it matter which one goes where? On page 59 of the Supplement, Bayliner suggests that "... the normal settings are Engine battery switch - Position 2, House battery switch - Position 1". I would suggest that, assuming that your two batteries are identical, then it doesn't really matter - it could just as easily be the opposite. But this is fine.

          **** The important thing to know, and remember, is what LOADS are being powered through which switch! ***

          If you label them as I suggested, it should be pretty obvious. Then operationally, your management becomes pretty simple. Let's go with Bayliner's recommendation. You get to the boat in the morning, and select position "2" on your upper switch, now labeled "PORT ENGINE". Now select position "1" on the lower switch, labeled "STARBOARD ENGINE/HOUSE". Start the engines and go boating. Each alternator charges it's associated battery while underway. Everybody's happy.

          Now you get to your favorite bay, drop the anchor and shutdown for the day. If you don't move the switches - and you shouldn't - what's powering your stereo, lights, refrigerator, etc.? The correct answer is obviously "Battery #1". So - you can, and should think of "Battery #1" as your HOUSE battery - that's what it's doing, powering all your house loads. And if you stay out there long enough, or overnight, then Battery #1 is probably going to be pretty discharged when it comes time to do it's other job - start the Starboard engine! As long as you understand this, and perhaps monitor the voltage with a properly installed digital voltmeter, this is perfectly manageable - because you have an almost fully-charged start battery (#2) to use for engine starting. So, when it's time to go, if your starboard engine does not start up normally, leave the switches alone, and simply start the port engine. Now you have an alternator online, providing charging current back to it's battery. Go to your battery selector switches, and select position #2 on the STARBOARD/HOUSE switch. (Do not change anything on the PORT ENGINE switch!) You are now connecting the starboard engine to the fully charged #2 battery, which is also receiving charging current from the port alternator (though not much at idle). Go ahead and start the starboard engine, which should have plenty of cranking power now.

          Last Step - before you forget - go back to the battery switch panel and rotate the STARBOARD/HOUSE switch counter-clockwise back to its normal position #1. USE CAUTION WHEN MOVING THIS SWITCH - you want to rotate it through the BOTH position at the top of the switch, NOT through the OFF position at the bottom. As you noted in your original post and has been pointed out by others, you never want to turn a battery switch to OFF, even momentarily, with the engine running. The switches are made with a "make before break" design so that rotating them from 1 - BOTH - 2 or vice versa can be done safely with the engine running and not interrupt the connection.

          You may notice that nowhere in this discussion is the use of the BOTH position mentioned, on either switch. That is not an oversight. Others may disagree, but personally - on a twin-engine boat with two charging sources - I would avoid using the BOTH position. There is simply no need for it, and it leads to the very real possibility of ending up dead on the water with two discharged batteries. I see it WAY too much. It doesn't take much imagination to see how this can happen - just consider if your STARBOARD/HOUSE switch was left inadvertently in the BOTH position in the scenario above.... what condition do you think both of your batteries would be the next morning? There might be a couple of scenarios (mostly involving inoperative equipment like a dead alternator) that would warrant using the both position on your boat, but trust me on this, you're better off avoiding it, at least until you have a solid understanding of your boats electrical system and related DC charging systems.

          Of course - the best solution is the addition of a large, dedicated deep-cycle house battery bank, with associated battery box, cabling, switch's, and charge relay(s) to take care of your house loads while cruising. That way your start batteries can remain isolated to their respective engine, and not be subject to sustained deep-cycle discharging that they were never intended to endure. Your battery management would also be much simplified. But this is a significant project that requires proper design and installation if you want it done right. If you intend to use your boat for anything other than day trips, I would encourage you to look into this. In the meantime - know what you've got, and you should be OK.

          My apologies for the rough drawings, but I'm already about 2 hours into this post and I don't have time to clean them up. Hopefully you'll get the idea.


          Seattle, WA
          2004 305
          350 MAG MPI, Bravo 3


          • mhopeng
            mhopeng commented
            Editing a comment
            Thanks for this post, it was extremely helpful and cleared up many questions. I am going to print it out and put it in the owner's manual.