NOVELTY - The battery pack has battery cells (1), an isolated liquid in which battery cells are soaked, and a battery box containing the isolated liquid and comprising box body (32) and cover plate (31). Electrical connection components (12) are disposed in battery pack and soaked in isolated liquid. A support frame (6) that supports battery cells overhead, and a collection portion are disposed at the bottom of battery box. A detection component, such as conductivity sensor, pH value sensor, fluorine selective electrode and/or liquid-level refraction sensor is disposed in the collection portion.    USE - Battery pack for e.g. electric vehicle, and electric bus.    ADVANTAGE - Provides safer battery pack since the battery calls are fixed more accurately by fixing the bottom surface of each battery cell to a cover plate of the battery box, and leaked electrolyte is enclosed in fire-retardant isolated liquid so that electrolyte is prevented from contacting with air and thus cannot be combusted even at a high temperature so as to avoid risks. Improves convenience of collection of leaked electrolyte since collection portion is V-shaped or U-shaped. Detecting at first time whether liquid leakage occurs to any of the battery cells in the battery box and sending an alert can improve the safety of the battery box. Electrolyte is accumulated into the collection portion disposed at the bottom of the battery box and is detected by the detection component disposed in the collection portion, and since electrolyte is a good electric conductor, the resistance value is detected to be smaller than threshold, and an alarm signal is sent by conductivity sensor to a vehicle control system and is displayed by an instrument panel, thus, the driver can be informed of whether there is a problem with the battery so as to perform maintenance and replacement in time and reduce the possibility of occurrence of risk.    DETAILED DESCRIPTION - The isolated liquid, such as fire-retardant and insulating liquid that has a specific gravity smaller than an electrolyte and is insoluble in electrolyte, is silicone oil or transformer oil or both. An INDEPENDENT CLAIM is also included for a liquid leakage detection method for battery pack.    DESCRIPTION OF DRAWING(S) - The drawing shows the perspective view of a batter box.    Battery cells (1)    Support frame (6)    Electrical connection components (12)    Cover plate (31)    Box body (32)