The battery is a rare pickup found in caves (in all depths). The battery can also be found in different Undersea Civilizations for purchase. It can be applied to an engine room console to give an extra unit of power to the applied console. When the player picks up the battery, it is recommended that they immediately head back to the sub to activate it, before continuing to explore, as, when the battery is being held, the player will not be able to use their items, and will drop the battery if they attempt to do so. Each console can have as many batteries as its maximum power allows (e.g. lights can have 1 battery, but engine can have up to 3).
The Battery will eventually run out of juice and disappear from the console it is in, so it may be advisable to save batteries for dangerous situations, such as bosses.
Update News Overview
New Special Cave Drop: The Battery! - This strange-looking electric capsule doesn't behave like most Vessel Upgrades you're used to - this fella needs to be picked up and plugged into a Power Console! Once plugged in, The Battery will constantly provide an external source of power to the console it's attached to, until it runs out of juice! Free up your energy costs and plug in a battery!
Note: bring a friend to watch your back when you are hauling a battery; these fellas are heavy and will take both your arms to lift!
Update Link (includes image): http://steamcommunity.com/gid/103582791455126886/announcements/detail/1438188152909674283