Multiple battery banks or one big one

[SV DestinyAscen]

One bank - one starter. If you're looking at the same overall capacity - the larger single bank will have a longer lifespan than two smaller banks that you're constantly deep cycling.

[Dulcesuenos]

Originally Posted by Thorne

Actually I said "While working" .... Details are important.

You did say the fighting a losing battle, and you run AC off your batteries? Not un heard of but does draw a lot of power. If your turning off your refrigeration each afternoon and run only an anchor light at night (an led one) than its possible to draw so little at night. Waking up with 90% SOC is hardly a bad thing/ losing battle

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[noelex 77]

Originally Posted by skipmac

Other than the ability to immediately switch one bank out of the system in the very remote chance that one battery shorts, what advantage do you see for having two banks?

I would not lightly dismiss this advantage. Sudden battery failure from a mechanism like an internal battery short is not unusual when offshore sailing. In rough conditions the battery plates have to withstand a lot of pounding. This is invariably when internal battery shorts occur. Unfortunatly it also the worse time for trying to diagnose and fix the problem especially as with a single battery bank this will mean turning off all the electronics including the autopilot and navigation lights. The battery bank is also subject to a deeper level of discharge than is seen at anchor further increasing the chance of a battery falure. With two battery banks it is much easier to identify if there is a problem. A defective battery can be isolated from the system with the flick of switch.

There are several other advantages. It is easier to equalise the batteries, or periodically get them up to a true 100% SOC. Both of these things can be difficult to do for a boat like mine that only connects to shore power every couple of years. Equalisation voltages can be damaging to electronics. Two battery banks enables batteries to be isolated while they are equalised, but the electronics can continue to function normally on the second bank. It creates redundant battery connections, as well as redundant main fuse and redundant main battery switch. Using batteries of different chemistry or age is much more practical. Finally trouble shooting of battery problems is easier.

Many cruising boats manage well with a single house battery bank. Two house banks are by no means essential, it is overkill for most boats that are marina hopping, but there are advantages. The cost to divide the house bank into two is minimal.

Unfortunately, there is a great deal of misunderstanding about boats with a dual house battery system. Most objections are based on the mistaken assumption that having two banks means they are always operated independently. Some posters in this thread are planning to use their batteries this way. This is almost always a bad idea because the capacity of the battery is related to the discharge rate. It is important to understand Peukert's law when dealing with lead acid batteries.

Used intelligently and correctly, two house battery banks are better than one. Modern boats are very dependent on electronics and for a very small additional cost two independent house battery systems can be created, adding a lot of versatility with almost no drawbacks.

[conachair]

Originally Posted by noelex 77

There are several other advantages. It is easier to equalise the batteries, or periodically get them up to a true 100% SOC. Both of these things can be difficult to do for a boat like mine that only connects to shore power every couple of years. Equalisation voltages can be damaging to electronics. Two battery banks enables batteries to be isolated while they are equalised, but the electronics can continue to function normally on the second bank. It creates redundant battery connections, as well as redundant main fuse and redundant main battery switch. Using batteries of different chemistry or age is much more practical. Finally trouble shooting of battery problems is easier.

+ 1!

Add to that making it easier to do a load test.

Maybe not such a big deal on non cruising boats, but having 2 switchable banks has many advantages living off the beaten track. Well worth a little extra wiring & a few switches.

[Maine Sail]

Originally Posted by Thorne

Actually I have been wrestling with this very thing.
1. 12 volt auto/marine batteries are setup to be able to produce huge starting amps for short periods of time. ( so you can start the engine ) When fully charged they can do this repeatedly with no ill effects. Asking a deep cycle golf cart battery to do this at all is Very Hard on them. ( You might get only a year of service from them )

Trojan Battery:

"Q: Can I use my deep-cycle battery as a starting battery?

A: Deep-cycle batteries can be used for engine starting but starting batteries should not be used for deep-cycle applications. A deep-cycle battery may have less cranking amps per pound than a starting battery, but in most cases a deep-cycle battery is still more than adequate for the purpose of starting an engine."

[Maine Sail]

Originally Posted by noelex 77

Used intelligently and correctly, two house battery banks are better than one. Modern boats are very dependent on electronics and for a very small additional cost two independent house battery systems can be created, adding a lot of versatility with almost no drawbacks.

Sadly this is not what most people who have two banks generally intend or desire to do. They generally want to alternate the banks. All you are doing is providing switching so that a battery bank can be taken out of the loop that is otherwise always one large bank pretty much always used together.

[noelex 77]

Originally Posted by Maine Sail

All you are doing is providing switching so that a battery bank can be taken out of the loop that is otherwise always one large bank pretty much always used together.

Precisely .

[conachair]

Originally Posted by Maine Sail

Trojan Battery:

"Q: Can I use my deep-cycle battery as a starting battery?

A: Deep-cycle batteries can be used for engine starting but starting batteries should not be used for deep-cycle applications. A deep-cycle battery may have less cranking amps per pound than a starting battery, but in most cases a deep-cycle battery is still more than adequate for the purpose of starting an engine."

And they even give data on it...

[Maine Sail]

This is the wiring I tend to prefer to use if an owner desires the ability to isolate series pairs of a house bank.

The isolation switches and busbar remain out of sight but easily accessible and the main ON/OFF is all you or guests see.

The bank is always in parallel unless you are servicing it, EQing or have a failure..

[ramblinrod]

Originally Posted by Thorne

As to my separate windless and starter batteries.....

They are currently 12 volt. They are connected by a set of # 6 or 4 wire that is 35 ft. long making it possible to "Charge the windless battery" but not "Run" the windless.

This is a serious safety hazard. A boat fire waiting to happen.

Develop a high impedance connection, or dead windlass battery, and all windlass current (plus dead windlass battery charge current) will be drawn through the #6 or # 4 AWG wire.

Common DIY mistake.

The only practical way to run cables from the house bank to the windlass (or windlass battery) using lighter gauge wires than will support the max current of the windlass is to install a current limiting charger like an echo or duo charger.

It has to be a very big boat (or windlass), for the advantages of a dedicated battery forward, to be more economical than running proper sized cables from the house bank.

[Olddave]

Originally Posted by jkindredpdx

Anyone want to talk about a less heated topic... like composting heads, anchoring, or AIS?

Go ahead, make my day

[sailorboy1]

I used to have 2 house banks that I always had both on. But I recently changed it to one bank, mainly due to solar charging.

I think as long as you understand what you are doing that it matters little whether you have 1 bank or 2 banks.

[ramblinrod]

Originally Posted by Dulcesuenos

This explains why the 6v true deep cycle batteries are better. It really comes down To increased plate thickness and increased cycle life Huge difference imhop in a constant use liveaboard or cruising application.

Deep Cycle Golf Cart Batteries For Power Storage



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I think this linked report is seriously flawed.

Sam's Club does not manufacture batteries. They rebrand batteries built by others. The 6 V batteries may be decent quality and the 12 volt batteries crap (as reflected by the price and specs.)

In one section the author states that one can't trust marketing hype, and in the next, the cost per a-hr comparison is performed using published specs.

This makes me seriously question the conclusions drawn.

For most reputable battery manufacturers, their Grp 27 has ~ 1200 w-hr capacity, and GC2 ~ 1290 w-hr.

If one does a fair comparison, chosing equal quality batteries to compare, I am confident the results would be much closer.

6 V golf cart batteries have to have heavier plates. They transfer much more current per cell. If the same plate thickness was used as in Grp 24s, they would fail very quickly. Grp 24s do not need such heavy plates. They do not transfer nearly the amount of current per cell. Note that similar quality grp 27 and GC2 having about the same w-hr ratings are about the same weight (meaning same amount of lead) indicating that they are pretty equal, just distributed differently due to the current per cell characteristics.

I think the term "true deep cycle" referring to GC2 over Grp 27 is a bit misleading.

I have yet to see an actual comparison under controlled conditions, producing equal stress on the batteries, that clearly indicates that golf cart batteries are superior.

I have seen many cases when individuals have invested in a modification or change to a system, that they declare a significant improvement, when in reality, it simply wasn't there, they are just justifying the expense in their own mind, and trying to influence others to make the same decision, further affirming their choice.

[a64pilot]

Originally Posted by skipmac

Hope there aren't too many out on the water that don't understand how this would work.

Other than the ability to immediately switch one bank out of the system in the very remote chance that one battery shorts, what advantage do you see for having two banks?

I have two banks, in slightly different locations, and the wiring for the switch for both banks was already there, for me it was easier to just leave them as two banks, but put the battery selector switch to both.
As far as not using the house bank to start an engine or run a Windlass, that is silly, my 660 AH bank would easily start a large Bulldozer, starting my baby Yanmar is child's play for it, and I'd say due to a lack of voltage drop that you want to run your windlass or thruster off the biggest bank you have, having one smaller battery just for those leads to a higher voltage drop and that leads to heat, which of course is bad.

[skipmac]

Originally Posted by noelex 77

I would not lightly dismiss this advantage. Sudden battery failure from a mechanism like an internal battery short is not unusual when offshore sailing. In rough conditions the battery plates have to withstand a lot of pounding. This is invariably when internal battery shorts occur. Unfortunatly it also the worse time for trying to diagnose and fix the problem especially as with a single battery bank this will mean turning off all the electronics including the autopilot and navigation lights. The battery bank is also subject to a deeper level of discharge than is seen at anchor further increasing the chance of a battery falure. With two battery banks it is much easier to identify if there is a problem. A defective battery can be isolated from the system with the flick of switch.

There are several other advantages. It is easier to equalise the batteries, or periodically get them up to a true 100% SOC. Both of these things can be difficult to do for a boat like mine that only connects to shore power every couple of years. Equalisation voltages can be damaging to electronics. Two battery banks enables batteries to be isolated while they are equalised, but the electronics can continue to function normally on the second bank. It creates redundant battery connections, as well as redundant main fuse and redundant main battery switch. Using batteries of different chemistry or age is much more practical. Finally trouble shooting of battery problems is easier.

Many cruising boats manage well with a single house battery bank. Two house banks are by no means essential, it is overkill for most boats that are marina hopping, but there are advantages. The cost to divide the house bank into two is minimal.

Unfortunately, there is a great deal of misunderstanding about boats with a dual house battery system. Most objections are based on the mistaken assumption that having two banks means they are always operated independently. Some posters in this thread are planning to use their batteries this way. This is almost always a bad idea because the capacity of the battery is related to the discharge rate. It is important to understand Peukert's law when dealing with lead acid batteries.

Used intelligently and correctly, two house battery banks are better than one. Modern boats are very dependent on electronics and for a very small additional cost two independent house battery systems can be created, adding a lot of versatility with almost no drawbacks.

Oh I am not dismissing the possibility of a battery short or the need to guard against it, although I'm not sure if I'm doing it lightly or not.

It is something that can and does happen but I'm not certain how large a risk it is. After all, it's never happened to me.

Seriously, a battery short could be a catastrophic event but what are the odds of one happening? I guess it comes down to the usual equation weighing the chance of occurrence against the ramifications if it does occur. However, if one tries to prepare and guard against every possible thing that might ever happen on a boat then he/she would never leave the dock. In my boat with three pairs of 6V batteries it would add a major complication to the wiring to isolate each pair with switches. To isolate each pair to allow equalization of individual banks while using another bank (which is certainly a good idea since, as you note, the high voltages are hard on some equipment) will also add additional wiring and switches.