Infusion

Infusion is best picked up early-game, as it does not work retroactively, only adding health for every kill after receiving the item. It is possible to farm large amounts of health from certain stages, including all stages early-game and in Boar Beach. The increase in max health per kill synchronizes well with as on every kill not only will your maximum health increase but you will also heal. Infusion makes farming more attractive as it increases your chances, even though it can still be time consuming to do so.

Using the Glass artifact, the Infusion item is incredibly useful, as the detrimental effect of Glass reducing your health to 10% of its original only applies to your normal health. Infusion gained health is not cut, allowing the player to get back to normal levels of health and beyond quickly.

Maximum amount of health is 9999. When used with, you can have more than 9999 hitpoints, but only due to the shield. You cannot increase health beyond 9999 via infusion.

Character Synergies
Although Infusion is a fundamental item on any character, it works best on high damage/high area of effect characters who can kill large groups of enemies quickly and frequently to maximize health (i.e. Acrid, Mercenary, Bandit, Loader).

Item Synergies
Note that getting multiple Infusions will increase the permanent health buff per kill, and in synergy with Bitter Root (which has a stack cap of 38, capping at 300% health), one can obtain 10-16 health per kill, resulting in huge health buffs throughout the game. This works best with the artifacts of Command (to get as many Bitter Roots as possible) and Glass (counteracts the fact that one has 10% health by maximizing health and still keeping the 500% damage).

Trivia

 * Health caps at 9999 hp, which is best achieved with multiple Infusions and >38 Bitter Roots.