Just for tests I have killed few UEV's without healing (by melee char). I hadn't Life Leach. I had Bushido and Chivalry but didn't used Confidence and Close Wounds. I hadn't any other healing skills. I didn't used potions. I had 4 HPR (from the slither and the crimson). I used a bladed staff. During a fight UEV drops my health from 140 to 70-90 hp.