This mod can be purchased unranked from the Void Trader Baro Ki'Teer for 220,000 Credits 220,000 and 300 Ducats 300. Note however that Baro Ki'Teer's stock changes with each appearance, and may not have this item available at every time.
Regen is a universal mod for both aggro-attracting Sentinels (Dethcube) along with utility Sentinels (Carrier and Shade) as they are able to be caught within line of fire from area-of-effect attacks.
Regen synergizes well with the Sentinel's Enhanced Vitality, as the modified maximum health is recognized as the current maximum health for the Regen ability to provide.
Gives the Sentinel 100 affinity for activating this ability.
This mod does not actually revive the Sentinel, but instead it automatically heals the Sentinel a certain percent depending on the fusion rank when it reaches 0 health.
Because the amount of health restored is scaled across all ranks, and given the higher base cost of Primed Regen, Regen is always a better choice up to rank 5. However, above rank 5, Primed Regen adds additional revives that Regen does not.
Full revival of a Warframe does not reset the regeneration count of the sentinel equipped with this mod.
Regen now grants temporary invulnerability to Sentinels on revive for a duration of one second + one second per rank of the mod. This means that with a maxed Primed Regen, you could see 11 seconds of invulnerability after the Regen occurs. (Listed in 19.6.2)