Health Boost I adds a segment of health and is one of the cheapest survival picks in the Combat tree. It opens once Sequence 1 is done.
Health Boost I sits at position 5 of 18 in the Combat tree. Unlocking Health Boost I takes 1 skill point. You need to complete Sequence 1 before you can buy it. Jacob and Evie each have their own skill tree, so you buy Health Boost I once for each twin.