Charger

In the Half-Life series, the Health and HEV Suit Chargers are devices that give the player health and armor points as long as he holds down the "use" key near them. However, these Chargers have a limited amount of supplies and will run out.

Health
In both games, Health Chargers are scattered throughout areas, and are placed around for the convince of staff in high-risk areas, such as in areas with dangerous creatures or machinery. The device can be used by anyone. The HL1 variant can has a keypad for dispensing a certain amount of healing (this doesn't affect gameplay), but the HL2 variant does not have one. Instead, it has a white line that gets smaller as more supplies are used up.

HEV Chargers
HEV Chargers appear in both games, but for completely different reasons. In Half-Life 1, there are dedicated HEV suit chargers scattered throughout the facility, hinting that HEV usage was widespread throughout the Black Mesa Research Facility. In addition, generic power sources (Olm's) can also be used to draw power for the HEV suit, though these only appear in the more-neglected areas of the facility. Dedicated PCV chargers are made, but they only appeared in key parts of the facility controlled by the military, mostly after the Resonance Cascade. In the neglected parts of the facility, there are old HEV Chargers that have a different shape. These usually work like the "newer" models, but some are prone to exploding.

In Half-Life 2, "HEV" chargers are actually generic power sources used by the Combine. The Mk V HEV suit has been designed to specifically accept power from these sources. The only "original" HEV Suit charger is a front plate that can be found in Black Mesa East and the White Forest base.

Gameplay
In Half-Life 1, Heath and HEV chargers are the primary source of health and armor throughout the game, especially in Hard mode. Medkits and Batteries do not give out enough health and armor to be effective long-term healing and protection.

Things have changed somewhat in Half-Life 2. Medkits now heal 25 health, irregardless of the diifculty level. This turns Medkits into the primary healing item. However, the HEV charger is still the primary source of armor, as Batteries are uncommon.

Trivia
Health and HEV chargers can be placed in Team Fortress Classic maps. They have much larger reserves than their Half-Life 1 versions.