Trusting you can also flick a switch to link your #2 and #3 batteries to use them as a starting power (just in case) then I cant see a problem.

Is that if one fails it will kill the other - better to have each isolated and separately chargeable though some sort of switching.

Your on the money Mitch

Battery bank 1- 1 x battery purely for starting charged via the alternator.

Battery bank 2- 2 x house batteries in parallel charged via your solar panel.

1-2-both switch to connect the two banks for emergency starting. 

240v two bank charger to charge and maintain both banks when boat is not in use.

If doing long runs you could add a DCDC charger too that switches the house bank charging from solar to alternator (quicker charge) while the engine is running and back to solar when the engine is shut off. 

 Thanks for the replys guys.

Swompa- The #2 & #3 with both be linked and when switched to the 2nd on the isolator it will pull from both the 2nd and 3rd battery.

Sunshine- Somehting I did think off  , I will be replacing the 2nd and 3rd with exactly the same CCA and brand new batterys so eliminating old and new batteries in parrallel and in the event they fail I'll crank off the 1st battery. The other way I can think is getting a new isolator 1,2,3 and replacing my current regulator to a redarc so I can solar feed two batteries at once. Personally I cant see how you can mantain 3 batteries on a trailer boat with out solar or running a 240v charger once home.

Stevo81- When hooking up the solar feed to the batteries in parallel do I connect positive to one battery and negative to the other battery?

Any point putting in a digital voltage read out, or is that just got show, as the LCD display for the engine show battery % ?

 How about using 2 VSRs?  

Example:

Starting battery -> vsr -> 1st house battery -> vsr -> 2nd house battery

So in theory, if you connect a solar charger to the crank battery, the first vsr will connect to the 1st house battery when the crank battery is full. When the 1st house battery is full, then the 2nd vsr will connect to the 2nd house battery to charge it. 

Hope I made sense? LOL

I've never done anything like that but in theory it should work...

Yeh i have triple battery setup. BEP+Ctek combo

Start -VSR- House ( these are switcahble and can be parralelled)

Standalone running 200w solar only, to run 2 x fridges. Is running a ctek so i can also run off the alternator if i feel the need. Have not felt the need yet!

Vinnie

 The key is a decent regulator here that will charge all batteries evenly with 3 step charging and prevent power from going back out through the solar panel at night, you get what you pay for with regulators though. Need something like this.

http://www.jaycar.com.au/Ecotech/Solar-Power/Solar-Charge-Controllers/12V-24V-30A-MPPT-Solar-Charge-Controller/p/MP3735

 Those bep vsr can be pointless at times, my bep vsr relay is always engaged linking the 2 batteries together at all time due to the high voltage in the calcium battery. Even when the motor is turned off it can remain engaged for days. (Unless you connect the red looped wire to the ignition)

In short it is pretty much running "both" battery at all times 

ill be be removing the vsr and installing a dcdc charger on the house , and keeping the house and start batts seperate  with a emergency parralel switch

You are right, the technically correct way is to join the batteries in parallel then hook your charge wires to the positive on one battery and the negative on the other, also you should hook the load onto the same terminals as the charge system. This does two things, it makes the load on each battery identical and also eliminates any chance of a poor connection.

I run up to 4 12v batteries in parallel in machinery without any problems and lets face it one will always fail before the other and when it does you will replace them both at the same time.

I have gone away from triple batteries.

Have just installed 2 big batteries instead. 1 x 270A 1700CCA House battery and 1 x 1000CCA start 130A Start battery.

Controlled with a Ctek Dual 250s with smart pass.

Has 200w solar.  House, start and emergency switches. Also runs 200w Solar!

Will post some pictures when i am finished.

I did start going down the 3 batteries route but either way you would need 2 VSRs or parralell batteries which defeated the purpose. Back to 2 is much simpler and at 270A the beers will be cold for weeks!

Cheers

" Any point putting in a digital voltage read out, or is that just got show, as the LCD display for the engine show battery %?"

I wondered the same thing. Hoping to revive this post with some opinion on the battery read out.

There is this type of thing that monitors everything

www.bluesea.com/products/1830/M2_DC_SoC_Monitor

or this simple battery condition guage

dh778tpvmt77t.cloudfront.net/images/products/1027B.jpg

I wonder how accurate the gauge is - does anyone use one? I don't see them on small boats very often, so I wonder if they are useless??

Got a 3 battery setup (Bank 1 - 1 x Crank, Bank 2 - 2 x House) running a EvaKool 110L fridge, so keen to keep an eye on battery levels..

 For those of you interested I recently done a 5 days trip to the Abrohlos.

Running 2x 40ltr Engels one on fridge and one on freezer.

2x century 730 marine pro batteries in parallel hooked up to 160w panel. 

Cranking off my optima starting battery and running around on that for 45mins to 1 hour to recharge it then switching to my

2nd battery's to charge them whilst trawling and finding ground.

It was quite overcasted most days but the batteries didn't skip a beat.

Not once did the Engels stop or batteries run out.

During the night at the anchorage we had every LED light on the boat on aswell as fresh water shower pumps and 12v vac pak machine for fillets.

Only thing I would wanna change is bigger and more panels in the event I don't run the boat during the day to top up batteries.

I did have a Honda generator and jump pack as back up however was never needed.