Battery switch position

[bsangs]

Wondering what the consensus is on the battery switch position. I have two deep cycle batteries, a battery charger for when connected to shore power, 55 amp alternator, and a 200w solar panel. I always keep the battery switch on "Both." The conflicting information on whether or not this is the best practice hurts my brain, but for two years that's how I've done it, with no repercussions. What does everyone around here tend to do?

 

[Slick470]

I usually just keep it on 1 when using the boat and I turn it to off when I leave. I'll switch over to bank 2 if 1 starts getting low, but that's pretty rare with my usage. I have a combiner that charges bank 2 off of bank 1. My solar panel is connected to bank 1 so with the combiner will charge both batteries regardless of switch position.

 

[Loren Beach]

Battery choice switch always on "1" for all house and starting needs. Position "2" is for our Emergency /Spare 12 volt battery.
Our House Bank (#1) is 260 AH, and the #2 Bank is a 12 volt spiral cell AGM. We can easily anchor out for three days on that house bank. No solar (altho that's more due to no real place for panels and a low desire for adding complexity that we have not needed.)

 

[peaman]

Wondering what the consensus is on the battery switch position. I have two deep cycle batteries, a battery charger for when connected to shore power, 55 amp alternator, and a 200w solar panel. I always keep the battery switch on "Both." The conflicting information on whether or not this is the best practice hurts my brain, but for two years that's how I've done it, with no repercussions. What does everyone around here tend to do?

Your practice is okay for day sailing, but can get you in trouble when cruising and away from shore power. With the batteries switched to "both", if they ever got too low to start the engine, you will have a problem. So for cruising, you should use one bank or the other except when under power, in which case you should switch back to "both".

I got nervous about the possibility of forgetting to switch batteries while cruising that I changed the power wiring completely to have dedicated start and house banks, and a battery switch that is either "on" or "off" except in emergencies. I did that before Spring launch and have really appreciated it. When I'm using the boat, the switch is "on", and it's "off" when I'm off. It did involve installation of a new charger (which I needed to do anyway) and running a new alternator output cable. With the addition of a flexible solar panel on my dodger, I rarely connect to shore power, which is an added bonus.

 

[bsangs]

Your practice is okay for day sailing, but can get you in trouble when cruising and away from shore power. With the batteries switched to "both", if they ever got too low to start the engine, you will have a problem. So for cruising, you should use one bank or the other except when under power, in which case you should switch back to "both".

I got nervous about the possibility of forgetting to switch batteries while cruising that I changed the power wiring completely to have dedicated start and house banks, and a battery switch that is either "on" or "off" except in emergencies. I did that before Spring launch and have really appreciated it. When I'm using the boat, the switch is "on", and it's "off" when I'm off. It did involve installation of a new charger (which I needed to do anyway) and running a new alternator output cable. With the addition of a flexible solar panel on my dodger, I rarely connect to shore power, which is an added bonus.

Interesting. We did a two-week cruise this season and I kept the switch on "Both" for the entire time. Never ran into an issue. I'd assumed that between the solar panel, running the engine - either while cruising or at anchor/mooring ball - and offloading many items like the coffee maker, phone/tablet/bluetooth speaker charging, rechargeable lights - to my portable battery "generator" that all would be well. Did I just get lucky? (Should add that there were some marina dock stops during the two weeks that allowed me to connect to shore power, but the majority of the cruise was on mooring balls.)

 

[Slick470]

I think a potential work around to having a dedicated "start" battery might be to keep one of those automotive jump start battery packs on board and use that to start the engine if you run the house bank down too far. You'd try to avoid using it, but as a backup option, it should work ok.

 

[Christian Williams]

The idea of the switch is to preserve one battery for emergency starting. Depletion of the "house" bank can be unexpected, simply the result of old batteries or leaving too many appliances on all night. Therefore an "extra" battery is kept in reserve and never to be used unless needed.

The house bank can have multiple batteries but the reserve is usually just one.

In my case I am always on Battery #2 (house, two batteries). For emergency starting (if house bank goes dead) I'd select Battery #1, which invokes the third battery only.

My boat is wired so shore power charges all three when the selector is set to #2. When motoring I switch to "Both" ("All") so the alternator charges all three.

Boats can be wired differently.

 

[peaman]

Did I just get lucky?

No. It all depends on your charge/discharge profile. I might have gone a bit overboard in my upgrades (though I have no regrets), because I had had an unnerving experience with an unexpectedly low battery, and I hadn't had my battery monitor for long enough to really know my own charge/discharge profile. But now, with everything done and tested in practice, including with the recently installed solar panel, I have few worries, and can verify battery status instantly. And I never need to wonder if the battery switch is in the right position.

 

[Pete the Cat]

I think a potential work around to having a dedicated "start" battery might be to keep one of those automotive jump start battery packs on board and use that to start the engine if you run the house bank down too far. You'd try to avoid using it, but as a backup option, it should work ok.

I honestly have no idea why folks carry a separate "start" battery these days. I have cruised (some years constantly in exotic places) for decades and never had the need, nor saw the sense in having a separate start battery. I have always had two banks and run them together all the time. If one ever went bad (like a bad cell shorting out or flattening both in some short situation--very unlikely without a fire) and both banks were depleted, they could be separated and (there might be some weird exception to this) you could expect that the "good" bank would recover enough to start the engine. Now, with the automotive jump starters, (I have used one on a car and have one on board) the idea of the complication of a starter battery and its compilations (for charging, isolation) in a two bank system seems even more absurd. I understand clearly why the folks selling electrical doodads want you to believe that you need one.

 

[Christian Williams]

I don't think a third battery is complicated. And my automotive jump starter is always dead just when I need to use it.

But it depends on the boat. The 38 has a handy compartment for a third battery under the nav seat, next to the house bank. On the 32-3 I carried a portable backup simply because there was no such obvious place.

 

[southofvictor]

A couple thoughts. A dedicated start battery can usually be smaller and less expensive than a high amp-hour deep cycle battery. Since it’s best practice for any battery bank with multiple batteries to be the same type, brand, voltage, and capacity that might lead to an isolated start battery charged on a separate circuit. There are ways to set this up with diodes instead of manual switches so you don’t have to worry about it, too.

Of course if you have a single bank and can keep it charged up that’s certainly the simplest way to go.

 

[bsangs]

Lots of great info here. Just as I expected. Thanks all.

 

[mjsouleman]

I just replaced the two deep cell batteries on Discovery (E-30+) with a started and a single deep cell. Switch 1 for started and two for deep cell. Recommendation was to switch to deep cell after starting. Discovery has very limited power draw from LED salon lighting, wind, depth, speed, radio, and an autopilot.

 

[Frank Langer]

I just replaced the two deep cell batteries on Discovery (E-30+) with a started and a single deep cell. Switch 1 for started and two for deep cell. Recommendation was to switch to deep cell after starting. Discovery has very limited power draw from LED salon lighting, wind, depth, speed, radio, and an autopilot.

Mark,
Interesting to note that there was no concern about different charge levels and requirements for a wet cell start battery and a deep cell house battery. Also, switching from one to the other while the engine/alternator is running is fine if your battery switch is a newer one designed for that. The older ones could burn out the alternator if the battery switch was moved from 1 to 2, and it only takes seconds for that to happen. Just a caution for those with the older red switches.
Frank

 

[mjsouleman]

Mark,
Interesting to note that there was no concern about different charge levels and requirements for a wet cell start battery and a deep cell house battery. Also, switching from one to the other while the engine/alternator is running is fine if your battery switch is a newer one designed for that. The older ones could burn out the alternator if the battery switch was moved from 1 to 2, and it only takes seconds for that to happen. Just a caution for those with the older red switches.
Frank

Thank you Frank,

I checked out the battery setup yesterday and a gotcha. When switched to the start battery position, I have no instruments. When switching to 1&2 position, I had instruments and was able to start the engine then quickly switched to the number 2 position (deep cell).

After not sailing for the better part of 2 years, I am relearning what I forgot or never know.

 

[Frank Langer]

Thank you Frank,

I checked out the battery setup yesterday and a gotcha. When switched to the start battery position, I have no instruments. When switching to 1&2 position, I had instruments and was able to start the engine then quickly switched to the number 2 position (deep cell).

After not sailing for the better part of 2 years, I am relearning what I forgot or never know.

Mark,
Have you considered starting the engine in the battery #2 position with the deep cell battery, saving the other start battery for emergency backup?
Frank

 

[southofvictor]

While on the subject of batteries I have a question on maximizing house bank amp hours. It seems like given our battery well size we may be able to get more Ah by installing two larger 6v batteries in series rather than two 12v batteries in parallel. One downside is battery weight (not necessarily overall but each unit). Another might (?) be that if one of the 6v batteries has something bad happen to it and the other survives we couldn’t limp by on just one 6v with our 12v system. Anyone have experience they can share toward making this kind of decision?

 

[reginaldobaker]

While on the subject of batteries I have a question on maximizing house bank amp hours. It seems like given our battery well size we may be able to get more Ah by installing two larger 6v batteries in series rather than two 12v batteries in parallel. One downside is battery weight (not necessarily overall but each unit). Another might (?) be that if one of the 6v batteries has something bad happen to it and the other survives we couldn’t limp by on just one 6v with our 12v system. Anyone have experience they can share toward making this kind of decision?

This is a fair question and have never really dug into it, here's a link [1] to and an excerpt from an RV forum discussing. There are Ah gains but possibly added "quirks" (rotating the 6v is mentioned). It could definitely work and am sure folks have done it - I personally think it's easier to stick with 12v

Your six volt (sic) pari is 230 amp hours

your 12 volt AGM pair, is 200 amp hours

Yes that's very close, enough (15%) to be "Significant" in a 10 percent world, but not enough to worry me.

Regarding the selector switch, I only use both batteries during starting.

[1] https://www.irv2.com/forums/f258/amp-hours-ah-for-6v-vs-12v-147442.html

 

[Loren Beach]

While on the subject of batteries I have a question on maximizing house bank amp hours. It seems like given our battery well size we may be able to get more Ah by installing two larger 6v batteries in series rather than two 12v batteries in parallel. One downside is battery weight (not necessarily overall but each unit). Another might (?) be that if one of the 6v batteries has something bad happen to it and the other survives we couldn’t limp by on just one 6v with our 12v system. Anyone have experience they can share toward making this kind of decision?

Our boat came from EY with a two "bank" system of two group 24 12-volt batteries. Wanting more AH for cruising, I installed a pair of 6-volt GC batteries where the factory had put the two smaller 12's. I built a box with a tray under the aft berth for an emergency 12 AGM battery. All loads including starting are from the main "house bank" which contains 260 AH. We have had to use the second battery only one time, when the main bank died without notice, after 9 seasons.
Note that our boat had enough height/room for the 6-volt GC batteries and some of the Ericson's might not. I have seen battery banks on a model 38-200, under the starboard settee, and there appeared to be room for some slightly taller batteries, but I did not measure the space.

 

[Second Star]

We have two deep cycle that are charged by the alternator, a solar panel or shore battery charger. When sailing or visiting frequently we switch from one battery to the other each day or two to keep both cycling through charge/discharge. At anchor we monitor the "in service" battery voltage to extend the time in service past one or two days to preserve the other for starting.