Abel will literally short-circuit from attempting to activate his nanomachines at a high % if he hasn't fed on enough vampire blood.
Esther shows just how selfless she is; being perfectly fine offering her blood to Ion. And this is with full knowledge that he could fatally drain her, due to the bullet making him ravenous.
Abel provides Ion with a flask of blood to quell the bloodlust. Suggesting Ion would have not drained Esther to the point of death; a flask is roughly the amount of a transfusion bag.