A lithium polymer battery, or more correctly lithium-ion polymer battery (abbreviated variously as LiPo, LIP, Li-poly and others), is a rechargeable battery of lithium-ion technology in a pouch format. Unlike cylindrical and prismatic cells, LiPos come in a soft package or pouch, which makes them lighter but also lack rigidity. The denomination “lithium polymer” has caused confusion among battery users. It may be interpreted in two ways. Originally, “lithium polymer” stood for a developing technology using a polymer electrolyte instead of the more common liquid electrolyte. The result is a “plastic” cell, which theoretically could be thin, flexible, and manufactured in different shapes, without risk of electrolyte leakage. This technology has not been fully developed and commercialized, and research is ongoing. The second meaning appeared when some manufacturers started applying the “polymer” denomination to lithium-ion cells in pouch format. This is the most extended use nowadays, where “polymer” went from indicating a “polymer electrolyte” to mean a “polymer casing”, that is, the soft, external pouch. While the design is usually flat, and lightweight, it is not a true polymer cell, as the electrolyte is still in liquid form, albeit it may be “plasticized” or “gelled” through a polymer additive. These cells are sometimes known as “LiPo”, however, from the technological point of view, they are the same as the ones marketed simply as “Li-ion”, as the underlying electrochemistry is the same. This article concerns the second, more extended meaning (among the general public), while the first meaning (understood in research and academia) is discussed only in the last section. The name “lithium polymer” (LiPo) is more widespread among users of radio-controlled models, where it may indicate a single cell or a battery pack with cells connected in series or parallel. The more general term “lithium-ion” (Li-ion) is used almost everywhere else, including consumer electronics such as mobile phones and notebook computers, and battery electric vehicles.