I'm not aware of battery technology that isn't lithium that would allow me to keep near 300ah of capacity and meet #1 without major surgery - such as my original idea, which is removing the air conditioner or taking all the storage under the setee.Steve,
There are really two goals here:
1) Getting the battery weight to the port side, near amidships and near the waterline, and away from the starboard, rear end of the boat, far from amidships, and maybe above the waterline.
2) Reducing the battery weight and perhaps adding to the performance and capacity.
Both are good objectives, but you can do one without the other. The second objective costs significantly more.
And by 300ah, I mean 80% of that capacity, not traditional 50% capacity with standard AGM batteries (or others) - I have carbon foam now, and can discharge them quite deeply.
But if I had lower amp hour requirements, for sure you could put an AGM battery in the stern bunk area, or under the settee for much less.