Battery blues. Or why I am never as clever as I thought I was.

[GILow]

Hi Cruisers,

I am in a mental bind over my battery bank. A quick summary is this: in about three and a half years from now (when my son has finished year 12) we will set off for a round Oz trip, plus maybe Vanuatu, NZ etc on a trip likely to be between one to three years in duration depending on how much we enjoy it.

The boat is a very low power consumption vessel and even the most pessimistic power budget tells me we will get away with a 400AH house battery bank, assuming 200AH useable capacity, though I would prefer to fit 600AH to nurse the batteries a little, as weight is not a concern.

We have 280 watts of solar and a large wind generator (300 watts) plus a decent quality 100 amp alternator to charge things. All currently work as they should, I have completely rewired the boat from scratch. The solar controller understands practically any battery chemistry and is programmable so battery choices are flexible. The wind gen is a fixed charge profile so requires manual monitoring. The alternator is externally regulated and manually switched.

The boat is currently a total dock queen, and because it will be a number of years before we got going I decided to be a cheapskate and bought a pair of really cheap 12v 120AH AGMs from a big online retailer here in Oz. My idea was that they would do for weekend sailing, then when we were ready to go I would toss them, fit 6 Trojan T105s, reprogram the solar regulator and get going.

Alas the AGMs have gone toes up in a year. (Probably less than a year actually, I only noticed they were dead when I did a longer than usual trip to Kangaroo Island recently.)

So now I have a dilemma. I am back to a situation where I don't want to fit the "real" battery bank because then it will have been sitting for more than three years before we use it, but the current battery bank can't even service the boat as a weekender. To complicate things, I need to be able to cannibalise the house battery bank in an emergency to create 24 volts if the engine bank dies, so that means at least two 12 v batteries are needed in the house bank.

Oh yeah, batteries are horribly expensive in Oz. current best price for the T105 I have been able to find is about AU$260 each. And I'd need four of those to create 24 volts.

What would you do in my situation?

Matt


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