[QUOTE=rdmiani;22192]
- I understand 6 volts batteries are not the same size, so fitting can be an issue.[/QUOTE]

There's a nice long writeup on this in the Upgrades section of the website
[url]http://www.c36ia.com/battery_support_repair[/url]
See also [url]http://www.c36ia.com/forums/showthread.php?t=2032&highlight=battery+swit...

[QUOTE=rdmiani;22192]
I'm curious to know how the battery selector switch would work. Is it as easy as Battery 1 is starting battery and Battery 2 is the house bank? And if that's the case, then if I had 2 12 volt batteries, I'd have to split them another way?[/QUOTE]

No sure what you mean by "I'd have to split them another way?".
Maybe Mainesail's excellent write-up (with diagrams) on the selector switch will clarify, available at [url]http://forums.catalina.sailboatowners.com/showthread.php?t=137615[/url]
There are lots of posts here as well on battery wiring, the selector switch, and so forth; if you haven't tried using the search function here its worth doing: here's a few: [url]http://www.c36ia.com/forums/showthread.php?t=1802&highlight=battery+swit...
[url]http://www.c36ia.com/forums/showthread.php?t=1188&highlight=battery+swit...
[url]http://www.c36ia.com/forums/showthread.php?t=1776&highlight=battery+swit...

Very good links from Matthew.

Once you've digested those, you might try these: Electrical 101 [url]http://c34.org/bbs/index.php/topic,5977.0.html[/url]

I switched to 6 volt after my original batteries failed after only 4 years. Lifting the old ones out convinced me of going 6 volt.

AGM batteries sound great, but a lot of the info is only hype and advertising. Maine Sail, who checks in here often, has a lot of great info and tests on his web sites and forum.

[URL="http://forums.catalina.sailboatowners.com/forumdisplay.php?f=135"]http://forums.catalina.sailboatowners.com/forumdisplay.php?f=135[/URL]

Either scroll down from Gene's link or use this one:

[url]http://forums.catalina.sailboatowners.com/showthread.php?t=124973[/url]

What this "proves" is that electrical stuff on boats HAS to be considered as an entire SYSTEM, not just "better" (?) batteries. Unless you install the appropriate charging system, nd most do not, AGMs are a horrible choice for recreational boaters.

[QUOTE=rdmiani;22205]
Matthew - My comment about having to split the two 12 volt batteries as a house bank has to do with using them both at the same time, all the time. Not sure if I got the terminology right, but I was thinking I'd need another switch or device to isolate one from the other.
[/QUOTE]

Ah, I think I understand your question now: You want to have a dedicated start battery, and as well the ability to have [U]two[/U] house banks?

Certainly this can be done. But would seem to mean more complicated wiring (and monitoring -- for example, the Victron BMV 602 is designed to monitor 1 house bank and 1 starter bank). From what I've seen on this site and in the technotes, most C36 owners who've revamped their systems seem to have gone with just 1 house bank (consisting of any number of 12V -or pairs of series-wired 6V - deep cycle batteries) and 1 smaller (group 24) 12v starter battery.

For what its worth, we adopted the system described at the end of Mainesail's excellent article
[url]http://forums.catalina.sailboatowners.com/showthread.php?t=137615[/url]
("Alternate Methods & Switches"). The Alternator output goes directly to the house bank, and the start battery gets its charging via an Automatic Combining Relay (in our instance, a Blue Seas SI series p/n 7610). We've found this system works very well; basically, we never have to bother with the selector switch anymore (unless we have a rundown battery someplace); charging selection takes place on its own, and the starter battery gets to be regularly exercised for its stated purpose.
[I]UPDATED 5/8/14 - Whilst trolling around in my computer looking for something entirely different (something I find myself doing all to often!), I came upon a diagram I'd prepared of our system back in 2012 (completely forgot about it), which is now attached.[/I]

(You might also want to check out Mainesail's article on battery monitors, at [url]www.pbase.com/mainecruising/battery_monitor[/url] )

The simple trick is to take your current two house bank arrangement, and make those batteries into one larger house bank, add a separate reserve or start bank and continue to use your 1-2-B switch. Your boat, your choice as to whether or not you want to go to a two switch design or just the 1-2-B, as discussed by Matthew and in the links I provided.

Here's why a larger house bank is better, also discussed in the Ample Power Primer.

Largest House Bank 101 (by Nigel Calder)

[url]http://c34.org/bbs/index.php/topic,5807.msg45046.html#msg45046[/url]

The Ample Power Primer [url]http://www.amplepower.com/primer/primer.pdf[/url]

Also discussed in the Electrical 101 link I provided earlier.

Good luck. Once you decide what you want to do, it's pretty easy.

[QUOTE=rdmiani;22213]Thanks Matthew...
If you run two 12v batteries in parallel to double your bank, how do you know the "health" of each battery separately? Can you wire a battery monitor to report the status of multiple batteries in a house bank separately, and the entire house bank as one bank, and the reserve battery as well?
[/QUOTE]
As I understand it (caveat -- I have absolutely [I]no[/I] qualifications whatsoever in this area, just passing along what I've read, for what its worth), a monitor is not going to tell you the "health" of the batteries. It gives you lots of data, such as the voltage, state of charge, amps going out or in, amp-hours consumed. And this data can be helpful in assessing whether you are using the batteries in a healthy manner (e.g., not overly deep discharging, etc.) But determining the battery's present overall state of "health" is a more complex thing, involving things like load testing, etc. See, e.g., [url]www.pacificpowerbatteries.com/aboutbatts/deep%20cycle%20battery%20faq/dc...

Even if you are merely seeking to "report the status of multiple batteries in a house bank separately", the only way to do this is to disconnect them from each other, since -- as you correctly surmise -- they will otherwise be essentially one large battery (just the way an individual battery is a collection of cells, of which the monitor cannot give individualized data). On the other hand, if the batteries that make up the house bank are all of the same age and capacity, there shouldn't be much need to that. Other than the (apparently rare) chance of a bad cell, if the collection of batteries that make up the housebank were collectively purchased new and used (or misused) together as one bank, they presumably should be in the same state of health -- whatever that might be.

On the third (?) hand, if you have one house bank and one starter battery -- as we do -- a monitor such as the Victron 602 (as we installed) can give separate data on each (the data it supplies for the house bank deep cycle batteries is more detailed than that supplied for the start battery, but that's fine for our purposes; you can take a look at Victron manual to get an idea of the sort of information it provides: [url]www.victronenergy.com/upload/documents/Manual-BMV-600S-600HS-602S-EN-NL-... )

[QUOTE=rdmiani;22213]
Also if I understand the postings, since your house bank may be 400 amp hours and your reserve bank or starting battery is only 100 amp hours, putting the battery switch on Both is probably not a good idea? [/QUOTE]

Its not so much because of the different AHs of the two banks, but rather because you want to make sure the reserve is in fact a reserve. Putting it on "both" utterly defeats the purpose -- if they're linked together they will be discharged down to same voltage, so that when your house bank hits 11.8V so will your starter battery. Then how do you crank your engine?

Unfortunately, you may have to use "Both" in order to charge both, the way the C36s come from the factory. The problem is that the tendency is to forget to move the switch away from "both" after charging is done (don't ask me how I know!) But if you use an ACR (battery combiner) then you no longer have to do so -- the ACR takes care of that for you even if the battery switch is left on the setting for the House bank only. And if you also wire the alternator output directly to the house bank (rather than through the battery switch), you've now eliminated the danger of frying the alternator's diodes if the battery switch is inadvertently move to "off" while the engine is running (and no, I haven't done that!), and completely converted it to a "use" switch rather than a "charge and use" switch.

[QUOTE=rdmiani;22213]
I have a good book on batteries and of course it's on the sailboat and not in my home library. ... [/QUOTE]

For deep analysis of this subject, I've found most helpful Nigel Calder's "Boatowner's Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat's Essential Systems" -- but, of course, its on the sailboat as well and not at home. But also helpful and a little less dense (and at hand at the moment) is Don Casey's "This Old Boat". Here's what he wrote regarding your earlier question:
"[I]... a dogma evolved that the best battery configuration was two battery banks used on a rotating basis. This is dead wrong You do need a separate battery for starting the engine, but whatever batteries you intend to use to supply your house power should be combined into a single bank. The logic for this is dead simple. The larger the bank, the shallower the discharge for a given time between charging. Shallower discharges extend battery life. Alternatively a larger bank allows you to extend the time between recharging, reducing wear and tear and operating costs. A larger bank will also accept charge at a higher rate, allowing your charging equipment to operate more efficiently and reducing the recharge time[/I]."

Matthew is spot on! :)

The Electrical 101 topic I linked you to has a link to the ample Power Primer, all about batteries. You don't need to go to your boat! :rolleyes:

Reading what every one has said about the danger of switching from 1 or 2 to both while the engine is running, I bought a new 1,2 both switch that will let you move from 1,2 to both with the engine running and not do damage . About 50$,

[QUOTE=William Miller;22226]Reading what every one has said about the danger of switching from 1 or 2 to both while the engine is running, I bought a new 1,2 both switch that will let you move from 1,2 to both with the engine running and not do damage . About 50$,[/QUOTE]

The error is not from switching between 1, 2 & BOTH it is that you may accidentally move it to OFF when doing so... All battery switches for at least the last 25+ years have been make before break...

[QUOTE=William Miller;22226]Reading what every one has said about the danger of switching from 1 or 2 to both while the engine is running, I bought a new 1,2 both switch that will let you move from 1,2 to both with the engine running and not do damage . About 50$,[/QUOTE]

The "point" of the links I have provided is what Matthew mentioned: changing the function of the OEM 1-2-B switch from a "charging" "decider" and use switch to just a use switch by moving the alternator output from the C post of the switch to the house bank.

Understanding this basic concept is the key to understanding how your boat is wired and "how it works."

Once you make this change you can turn the switch to OFF and not fry alternator diodes.