Thanks for an entertaining game.
I’m not sure what the rules for loosing a battle are, but today I managed to get to the “Defeat” screen, where I had one (heavily damaged) cruiser and a dozen or two fighters left. The enemy had about 5 cruisers left. That might sound like bad odds for me, but the auto-repair systems on my cruiser, together with a cloaking shield, kept it alive for long enough to have the fighters do strafing runs and destroy out the enemy.
So the conclusion of the battle was that I wiped out the enemy, but still lost. I believe that should be regarded as a bug.