So, i've been playing for a while, got a herculean, and tried multiple times to attack the phanon corps (had to reload a bunch because they were much stronger than i expected). One thing i noticed was that sometimes, either when i fought and had to emergency jump the herculean or when i just straight up won the fight agaisnt phanon, seemingly after a random amount of time the herculean started taking damage, as in, first it's shields start draining, then the armor, and lastly the hull. Eventually this triggers the passive ability that heals the herculean, but then it continues taking damage until it eventually dies. The only case where I managed to heal it was when I won the fight agaisnt phanon, and then took it to one of my starbases, mind you, i had to try with multiple starbases till i found the one that started healing it.

Now that it has been fully healed it stopped taking damage from nowhere, but if I were playing ironman, that herculean would've been dead, even if it got away from the fight in time.