Battery Bank Expansion

[Harry Brown]

I am looking for some information regarding battery banks on your Yachts.
It appears that at present (factory fit), I have two 140 AH leisure batteries both with separate isolation switches at the Nav station.
What I don’t understand is, why have 2 separate banks (apart from redundancy), why not have 1 bank with twice the capacity?
I would like to replace these 2 batteries with new ones and increase the capacity considerably. i.e. probably having 6 Trojans AGMs, or maybe LiFePO4 (but that’s another post!) .
So should I convert the existing wiring so that I will have 1 bank at say ~600 AH, or 2 banks at ~300 AH?
To me it seems better to have one 600 AH bank?
What am I missing here, why have 2 very small banks? What have you guys done in regards to battery bank expansion, if you have a similar 2 bank system?

Hope that all makes sense!
Thanks in advance.

[undercutter]

I believe the general thought process was to have two separate banks so that you never find yourself in a situation where you have completely flattened all your batteries. This of course limits you to half of your actual capacity. This was more critical where you used the house bank for starter batteries as well.

This situation is not very common any more but the thinking still prevails.

Also solar has significantly reduced the potential for draining battery banks.

We had 2 banks of 450 amp hrs each and I combined them to create one bank. We also have separate start battery as well as separate bank for the bowthruster. The house bank is T105's, the starter battery is an 8D calcium and the bowthruster batteries are dry spiral cranking batteries as they are mounted under the forward berth and wanted to ensure no leakage or fuming.

This can create some charging issues with separate charging sources to ensure that they all get the right voltages.

As long as you have a separate start battery I see no reason to maintain 2 distinct house banks.

[Terra Nova]

Best is one large house bank plus a start battery.

[Stu Jackson]

Originally Posted by Terra Nova

Best is one large house bank plus a start battery.

Here's why:

Largest House Bank 101 (by Nigel Calder)

stereo-battery connection

Having a small separate reserve or start bank is for redundancy and emergencies if the house bank fails for any reason (wiring, busted battery, etc.).