The origin of this object is shrouded in scientific mystery. Its clear that its made in part by di-electric elements, but science does not know the physical conditions in which it is formed. - Electro battery in-game description
When wearing this artifact the denaturalization of proteins happens slower. In other words, the flesh is able to endure higher temperatures and burns less. In itself it is an expensive and rare thing. - Fire battery in-game description
S.T.A.L.K.E.R.: Shadow of Chernobyl has two distinct Battery artifacts that share the same name but different description. The first is spawned by Burner anomalies and has an identical appearance to the Spring artifact, the only difference being the different texture, and gives fire protection. The second is spawned in gravitational anomalies, has the same appearance than its other renditions and gives electrical protection.
Both batteries give a +30% bonus in fire or electrical protection, and have no downsides whatsoever. This makes each type a valuable artifact to use through anomalies, especially when combined. As well, each sort of battery can enable suit repairing if the player combines four or more of them: four Electro batteries enable suit repair in Electro anomalies, four Flame batteries enable suit repair in Burner anomalies.
One other can be found in the lake in Agroprom, near the north shore.
Another can be found in the Red Forest, northwest of the anomaly cluster where the Goldfish is located. It lays in the south-western part of the map, if the player goes deep in the forest after encountering the first Monolith sniper (standing on a trailer), near a cluster of Springboard anomalies on the map border.
A third Flame Battery is located a couple of meters away from the Electro Battery in the Red Forest. It is well camouflaged, spends most of its cycle under the leaves and only pokes out above for about one-third of its cycle. While under the leaves the 'proximity detector' will not indicate its presence. There is also a Spring close-by performing a similar cyclical behaviour. Best located in afternoon / early evening hours. In order to get the artifact, the player must run towards it and pick it up very fast, as it will sink into the ground once approached.
The origin of this item remains a scientific enigma. It is only known that its composition includes dielectric elements, but scientists have yet to identify the exact physical conditions required for its formation. The artifact is popular in the Zone and valued by its residents and visitors for its restorative abilities. Emits radiation. - In-game description
The Battery returns in S.T.A.L.K.E.R.: Clear Sky, assuming the appearance of the electro battery from Shadow of Chernobyl. The Battery provides a +2 in endurance regeneration, allowing the player to run for more time before having to rest, although it also gives a +2 in radiation making the artifact semi-useful.
The composition of this artifact includes electrostatic elements, but scientists have yet to identify the exact physical conditions required for its formation. The artifact is popular in the Zone and valued by its residents and visitors for its energizing properties, although it can tire the body out through prolonged use. Emits radiation. - In-game description
The Battery returns in S.T.A.L.K.E.R.: Call of Pripyat, giving a +2 in endurance regenration and a +1 in radiation. The boost given is nearly unsignificant, meaning the player could well sell it and buy something more helpful.
The appearance of the Battery, Shell and Spring artifacts may be based on the "Full Empty" and "Empty", which are artifacts described in the book Roadside Picnic by Arkady & Boris Strugatsky - which served as an inspiration for the S.T.A.L.K.E.R. series. "Empties" are described as two copper-colored discs held together by an invisible, passable, but not separable field. "Full Empties" are described, again, as two copper-colored discs held together instead by a bluish material inbetween the discs.