One
Hi guy,
You only need one Odyssey and it's around one third the size of your Concorde and also around 680 amp cranking ability! We have a strong 0-360 with a Catto prop and it spins it fast! It is not a "wet" baterry and can even be laid on its side (from what I've been told).
Some guys want redundancy and they use two batteries....the second one on its own circuit with another switch (in case they lose the primary electrical system).....for the guys with 'glass instrument panels and a must for the guys who use automobile engines like the computer driven Eggenfellner Subarus.
Regards,