Healthy is a Defensive Upgrade.
Gives the soldier unlimited health regeneration. The soldier will keep slightly healing all the time, as if he/she was injured. It doesn't have Equipment version, but it can be get in the Slot Machine like all other upgrades. It is good for disabling the Unhealthy Flaw. However, Repair Bots is the better upgrade for killing that flaw.
Healthy upgrade can be used by Wesley, Mayday and Nathan. Fatale and Tower both have all defensive upgrade, but can't use this one.