Liquid batteries, distinct from traditional batteries, utilize a liquid redox couple for energy storage. These batteries, such as soluble iron/soluble chromium types, feature two solutions separated by a membrane, allowing for efficient energy transfer. Recent advancements include the use of vanadium II/vanadium III as a redox couple. While flexible polymer batteries exist, the concept of liquid batteries may refer to these innovative designs rather than conventional lead-acid batteries. The discussion highlights the need for clarity on the specific technology referenced in products like the Nokia 888, which is noted for its slim, foldable design.