How To Use Battery 1 and 2 - Conflicting Info - Please help!

BenningtonWA

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I bought my Bennington at the end of last summer so was only able spend a few weeks on it before storing it for the winter. When we bought it from a private party, they said to run the engines with both batteries (1 & 2) at all times. When we had the boat winterized the service tech at the Bennington dealership said to only run one battery at a time. Now, I am having the boat prepped for summer and a different tech (same dealership) said to run with both batteries at the same time. I am super confused and I don't want to mess up my boat. Any thoughts? Thank you in advance.

Bennington 2572 QCW
Yamaha 350
 

royal4

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I run mine with both batteries while underway to charge both batteries. If I'm just cove hopping I may just use one but when I'm going to be driving for 10-20 minutes it's both. When I stop someplace to hang out I switch to just one battery for stereo etc.. I don't want both going dead while listening to tunes and then be out of luck starting it for the trip home. ADD: I switch from 1 to both or 2 to both while underway with no problems. I have heard never switch to off while running so I'm careful when I do switch while underway. The smart way is only switch when stopped but sometimes I forget to put it on both until underway.
 
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Remediation

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There is no right way. The only rule is never switch while the engine is running. My rule is to turn the switch to off when done for the trip. When I get in the boat, I switch to all so both batteries will charge. If I am going to play the music for hours at high volume and big amps I would switch to the house battery to isolate the starting battery. Since I never do that I just leave it on all and know I have 1600 amps of starting power. Keep life simple.
 

Mike31406

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I do the same as many above, both for running, one for anchored listening to radio.
 

Magician

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I run and start on a single battery. I never run both at the same time. I was told that the charger/alternator on the engine isn’t rated to charge both batteries at the same time and you could damage it?
Just how I roll.

I‘ve switched while running but have never switched to off, in other words I’ve switched from #1 to #2 or vice versa but I went thru 1/2 to get there
 

BigKahuna

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Confused also. Never had a duel battery set up. Dealership told me to switch to both (A&B) batteries when entering the boat for the day and switching both to OFF at the end of the day. My old boat mechanic and a few friends have told me........ Knucklehead, why would you use both batteries all the time??? If you kill them both you're going to be stuck! Why do you think they give you 2 ??? Alternate usage. Makes sense.......
 

Vikingstaff

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I run as most mentioned above based on dealer technician advise when we bought it. set to 1+2 under normal operation and cruising. Isolate to one battery when motor off and listening to music. Switch to off at end of the day.

Never heard of motor/alternator issue that Magician mentions. If that can be a concern, I wonder if that would be motor/manufacturer dependent? That said, no one has ever mentioned that concern to me before.
 

Jack M

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I also go to my destination with both on . While at the sand bar, I switch one to off . I also have invested in a portable jump starter
 

BigKahuna

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I also go to my destination with both on . While at the sand bar, I switch one to off . I also have invested in a portable jump starter
Yup I've got a jump pack we used to bring on my old boat. But I figured I didn't need it with 2 batteries now.
 

Magician

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I tend to look at it this way, in the automotive industry if you specify a truck with two batteries don’t they also recommend a second alternator? There are different size(size referring to amp output) alternators?
Im just saying it’s how I look at the two vs one battery setup for how I use mine. One trip I start and run on one, the next I’ll start and run on two. Plus I keep my batteries on a charger most of the time.
 

Bill N

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It's NOT harder on an alternator to charge two batteries. Think of the alternator as a pump and your batteries as tanks. The pump doesn't care if it's filling one tank or ten tanks, either way it will stop pumping when they are full and begin pumping again as levels lower.
 

Bill N

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As mentioned, rocking out to the stereo while stopped is the most obvious use for selective battery use.
Also keep in mind that while idling along slowly your alternator output can be lower than your power consumption due to draw from power steering, stereo, lights, refrigerator/appliances, GPS units, chargers, converters etc. So it is indeed possible to drain a battery while underway, making having a second fully charged battery very important.
Someone mentioned having a portable jump-starter. I keep one in every vehicle! I've been able to save my own day at the lake as well as saving other boaters day! Nothing like the look on some stranger's kid's faces turning from disappointment to delight!
 

kaydano

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I can't say this enough... A simple charging relay automates all this. You can't forget any step in the process because it does it all automatically.

If you want to be able to completely disconnect the batteries at the end of each trip, add a switch with the relay. But, you will have to reprogram the stereo each time.

You'll only drain the house battery with parasitic draw anyway. The relay switches off the starting battery at the end of your trip.

The peace of mind knowing I'll always have a fresh battery without relying on my memory to ensure that is the best $100 I ever spent on our boat.
 
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Michiman

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I can't remember what I went into the bathroom to do so I'm certainly not going to remember to switch my batteries when I leave the sandbar. As such, from the moment I install them in the spring to the time I take them out in the fall, I leave it on A+B or 1+2 and have never had a problem. Now, if you're running a crazy amped up stereo system the sucks all kinds of power, then you will probably want to do some switching, but if you have a more normal radio (I also have a powered subwoofer), then you should have no problem getting started, even after hours of jamming to your favorite tunes while enjoying the boating lifestyle. Just my two cents and 30 some years experience. I will say that when my batteries get to be five to six years old, I'll take them to the local battery store and have them tested at the beginning of the season, just to make sure they're still viable.
 

GWLK

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A big LOL Michiman. I used to run on battery #1 during the week and battery #2 on the weekends. But then around Tuesday I would check to to what battery I was on, it would be battery #1, but then I couldn't remember if I used battery #2 on the weekend. So, now I'm with Michiman, I leave the battery switch on 1 + 2. Got to simplify things when you get older.
 

Magician

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Okay, so when that alternator has run twice as long to charge two vs one, that isn’t more wear? Seriously, there are more than a few different versions of why is right and clearly there are those who have had no issues running both ways. I simply gave what I know and have learned in all my time on the water. Maybe I should’ve prefaced it with “this what I do based off of what has worked for me for 15 years.”
 

Nautical

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It's personal preference really but what makes most sense to me, since 1 nearly dead battery can still start the engine, is to just run it on 1 battery and leave the other as a backup which is probably why this feature was conceived in the first place.

Or, you can travel on 1 and switch to 2 if you plan on 10 hours of being anchored with the radio and/or other accessories on but this would be more of a pain because you'd be switching it all of the time.

I run it on 1 all of the time for a month, then switch to 2 for the next month. You can do odd/even months to match which battery you use and it would be that much easier. Since I bought the boat new, I never even bother to ever turn it to OFF because I don't care if I drain one battery because I have the other. THIS way I'm only touching the switch once a month!

As for charging, I could be wrong, and several dealers who told me this could also be wrong, but they insist both batteries always get charged regardless of what position the switch is turned to. However, I was also told by several dealers every boat was wired so that the bilge pump would come on with the float if the water got too high even if the battery switch was in the off position but I've seen a few boats where this is not the case.

Here is an article on all of this: https://www.boattest.com/view-news/3084_solving-the-battery-switch-dilemma

That article was written for a boat that has shore power and he mentions that underway only the battery selected will be charged but if the dealers I've worked with are right then our charging should be as if we're on shore power. The article does mention the ONLY time you should use BOTH is if you have TWO weak batteries and are trying to start the engine. Otherwise never on both.
 
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Magician

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That makes perfect sense and is pretty close to what I do and have done. I’ll check next weekend and confirm if my boat charges both batteries when only one is selected.
 

BulldogsCadillac

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Yup I've got a jump pack we used to bring on my old boat. But I figured I didn't need it with 2 batteries now.
Ha! I had 4 big batteries and still brought my booster battery!! Now I will add that it was mostly for filling the tubes and if I needed to boost a fellow boater!

As for the switch, I will add this, the motor does NOT charge both banks regardless of switch selection, if it does, then it's wired wrong. I know this because I had a Victron battery monitor that I could see voltage levels of both banks. As for burning out the alternator, it was told to me that it is possible, but ONLY in special circumstances. For example, I had 3 group 31 Northstar batteries for the stereo, and a group 24 for my starting / house battery. These are TPPL batteries that can absorb huge amounts of current, fast! Problem being that (to go with the pump analogy) it would be like a garden hose feeding into a sewer pipe. Normal batteries simply cannot absorb the charge as fast so you will never have a problem with having the switch on 1+2. I had my stereo isolated to battery bank 2 completely for this reason, with a separate shore charger for this reason. I DID however wire it into the switch in case my starting battery ever failed I could put to combined and start.

I will add that at first start up (in normal boats applications) I would never put the switch to 1+2, reason being if you have one dead or bad battery, they will equalize and you will then have TWO dead batteries. Far better to select either one OR two to start, then once running switch to 1+2 (never going through OFF position to get there while motor running) to charge both banks. Just my opinion, but I did spend a lot of time thinking about it!
 
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