Do off-type defense do any thing in battle? I have the impression that it does nothing.
It does nothing.
How does does defenses work? I find it difficult to get good information on this.
Well, if you have a kinetic weapon which does X damage, it will remove X/2 points of defense instead of X hull points, if there is kinetic defense (regardless how much, you can keep 1000 damage kinetic blast from damaging the hull with a single point of kinetic defense).
The defense points of all types are completely regenerated after each battle.
Ah hell. Might as well explain to me ship combat works. Start to finish.
Duh,... where to start...
1) Ships are simulated to be at a certain distance (depends on ship role Capital, Escort, etc. ) to the enemy fleet at the start of the battle and will move towards each other
Exception: support ships. They stay where they are. If you have ever seen your frigates circling an enemy transport but not shoot it for some time, than that's because in the actual simulation they are not close to the transport yet, even though they are shown to be close.
2) Depending on your ships role, it will have a certain order in which they will target enemy ships of certain roles. I don't know how it decides between targets of the same role.
Example: Your Escort ship could be shooting an enemy capital, assault or escort ship. It will target the assault ship first and if it lives long enough it will proceed to shoot first the other escort ship and then the capital ship.
Example 2: your Assault ship will first come into range to fire at another assault ship. It will do so. But soon after it gets in range to shoot at enemy escorts. It will start targetting the escorts instead.
3) Weapons are fired not individually, but in salvos. Your 5 doomrays will not deal 5 times 32 damage, but rather 160 damage once. Remember what I said above? Yup, it will be blocked by a single shield point instead of 1 shield point blocking 32 damage and 4 attacks damaging the hull. The whole salvo. However you can split weapon types. If you have 3 missile launchers, 4 kinetic guns and 2 beam weapons, you will not fire 1 salvo with all of them, but each of the weapon types will fire salvos independently of each other. Keep this in mind when fighting fleets of many smaller ships.
I guess that's the gist of it.