Underwater device lithium battery system and underwater device

The invention relates to the technical field of batteries, and discloses an underwater device lithium battery system and an underwater device. The lithium battery system comprises a battery shell, a plurality of battery modules, an insulating thermal isolation unit, a thermal insulation plate and a fixed guide rail, the plurality of battery modules are arranged in the battery shell, the fixed guide rail is used for fixing the plurality of battery modules, each battery module comprises a battery cell and a nickel sheet arranged on the battery cell, and the nickel sheet is arranged on the battery cell. The plurality of battery modules are connected in series and in parallel through the nickel sheets, the heat insulation plates are arranged between the adjacent battery modules, the positive electrode and the negative electrode of each battery module are provided with the insulation heat isolation units, and each insulation heat isolation unit comprises an insulation plate, a directional heat conduction plate and