Do they make much difference? I end up using barrier a lot.

Battle cards are almost the only way you can directly affect the outcome of a battle, and yeah, used properly they can make a fairly enormous difference. A successfully played "Short Circuit" during the long-range phase can help you maximize your damage if you've chosen long-range weapons for your fleet. The "Barrier" is a very useful general-purpose card in early battles, but those extra 50 hit points just don't count for as much as the fleet sizes grow and the weapons become more deadly; the "Nano-Repair Systems" card becomes a better general defense later in the game. The "Offensive Retreat" card becomes vital if you are fighting a holding action against an invading force: you can send whatever fleet you've currently got out to the invaders, do a single round of damage to them, and then retreat and repair your forces. Hopefully they won't be able to repair if they are busy trying to conquer one of your systems, so you'll be able to fight a war of attrition against them. And, of course, a highly-skilled hero will have access to some incredibly powerful dust-fueled cards...



So yeah, a properly played card, taking into full account how it helps your fleet and hinders your opponent's, can significantly alter the results of a battle.

i use them situationally until i got a sufficient tech gap over the AI and after that I leave them blank because its too many clicks to set them when they aren't needed.

Most commonly i use the engineering card that gives repair (edit: Its called nano repair), its a hard one to counter, counters common AI choices, and provides repair to my ships

Once I have a mid-level pilot, most of my battles use one of two strategies:



Contested battle: 1. Dust Barrier 2. Nano Repair 3. Nano Repair. Because of the power and design of my ships, I expect most battles to be over before medium-range combat.

Uncontested battle: 1. Nano Repair. If I'm fighting a scout or invasion fleet, the battle will be over before medium-range combat.



Early in the game before my pilot (I play a custom race that guarantees me a pilot) has dust barrier, there can be a little more guessing.



Most of my battles are also usually done on auto. However, if it's a super tough battle, I might fight it manually. Since all of my weapons are long-range, I might need to retreat if I don't slaughter the vast majority of the enemy fleet in the long-range phase.