A sealed deep cycle battery is a battery designed to be periodically deeply discharged using most of its capacity. The term has traditionally been used primarily for lead-acid batteries of the same form factor as car batteries; such batteries are designed to provide only a fraction of the capacity in brief bursts of high current compared to starter or "starter" car batteries to start the engine.

    For lead-acid deep cycle batteries, there is an inverse relationship between the depth of discharge (DOD) of the battery and the number of charges and discharge cycles it can perform; the average "depth of discharge" is about 50% and is recommended as the best choice for storage versus cost.

    Deep-cycle lead-acid batteries are generally divided into two distinct categories; flooded (FLA) and valve-regulated lead-acid (VRLA), where VRLA types are further subdivided into absorbed glass mat (AGM) and gel types. The reinforcement of the absorbent glass mat partition helps reduce damage from spills and shocks. In addition, flooded deep cycle batteries can be classified into the subcategories of tube plating Opz or plate plating. This difference usually affects the cycle life and performance of the battery.

    "Submerged" is because this type of battery contains a certain amount of electrolyte so the plates are completely submerged. The electrolyte level should be above the top of the plates to act as a reservoir to ensure that water loss during charging does not lower the level below the top of the plates and cause damage. A flooded battery will decompose some water from the electrolyte during charging, so regular maintenance of a flooded battery requires checking the electrolyte level and adding water. The main failure modes of deep cycle batteries are the loss of active material due to plate peeling and corrosion of the internal gate supporting the active material. The capacity of deep cycle batteries is often limited by electrolyte capacity rather than plate quality to increase life expectancy.

    Changshu Wanlong Power Technology R&D Co., Ltd. is a lead-acid battery manufacturer and storage battery manufacturer from China. The company sells 12v deep cycle gel batteries and sealed gel batteries all year round.