What is claimed is:1. A battery system for an electric vehicle, comprising:at least one battery module including a plurality of battery cells, and an outer casing which defines therein an accommodation space for accommodation of said battery cells, and which is configured to permit a thermal management liquid to flow through said accommodation space to thereby provide thermal management to said battery cells;a management module which includes at least one sensing unit and which is coupled to said battery module to permit said sensing unit to be submerged in the thermal management liquid for collecting information of said battery cells and the thermal management liquid,wherein each of said battery cells has a first terminal and a second terminal, and said battery module further includes a first connection bar unit which is configured to electrically connect said first terminals of said battery cells together, and a second connection bar unit which is configured to electrically connect said second terminals of said battery cells together; andwherein said battery system comprises a plurality of said battery modules, said battery modules being stacked on each other to permit said battery cells of said battery modules to be electrically connected to each other through said first and second connection bar units, and to permit the thermal management liquid to flow through said accommodation spaces of said outer casings of said battery modules in sequence, said management module further includinga housing defining an inner chamber therein, and coupled to a leading or trailing one of said battery modules to permit the thermal management liquid to flow through said inner chamber, anda management circuit board which is mounted inside said inner chamber to be submerged in the thermal management liquid, and which functions to manage the information received from said sensing unit.2. The battery system according to claim 1, wherein said housing is coupled to said outer casing of the leading one of said battery modules to permit the thermal management liquid in said inner chamber to be introduced into said accommodation space of the leading one of said battery modules.3. The battery system according to claim 2, wherein said first connection bar unit has a plurality of first connection bars, and said sensing unit includesa connectivity sensor which is mounted on said management circuit board, and which is electrically connected to two of said first connection bars of the leading one of said battery modules for detecting an electrical resistance between said two of said first connection bars,a flow meter mounted on said management circuit board for detecting a flow rate of the thermal management liquid,a plurality of pressure sensors which are disposed respectively in said accommodation spaces of said battery modules for detecting liquid pressures of the thermal management liquid inside said accommodation spaces, respectively, and which are electrically connected to said management circuit board to permit data communication between said pressure sensors and said management circuit board; anda plurality of temperature sensors which are disposed respectively in said accommodation spaces for detecting temperatures of the thermal management liquid inside said accommodation spaces, respectively, and which are electrically connected to said management circuit board to permit data communication between said temperature sensors and said management circuit board.4. The battery system according to claim 3, wherein said pressure sensors are atmospheric MEMS sensors.5. A battery system for an electric vehicle, comprising:at least one battery module including a plurality of battery cells, and an outer casing which defines therein an accommodation space for accommodation of said battery cells, and which is configured to permit a thermal management liquid to flow through said accommodation space to thereby provide thermal management to said battery cells;a management module which includes at least one sensing unit and which is coupled to said battery module to permit said sensing unit to be submerged in the thermal management liquid for collecting information of said battery cells and the thermal management liquid,wherein each of said battery cells has a first terminal and a second terminal, and said battery module further includes a first connection bar unit which is configured to electrically connect said first terminals of said battery cells together, and a second connection bar unit which is configured to electrically connect said second terminals of said battery cells together;wherein said battery system comprises a plurality of said battery modules, said battery modules being stacked on each other to permit said battery cells of said battery modules to be electrically connected to each other through said first and second connection bar units, and to permit the thermal management liquid to flow through said accommodation spaces of said outer casings of said battery modules in sequence, said management module further includinga housing defining an inner chamber therein, and coupled to a leading or trailing one of said battery modules to permit the thermal management liquid to flow through said inner chamber, anda management circuit board which is mounted inside said inner chamber to be submerged in the thermal management liquid, and which functions to manage the information received from said sensing unit;wherein said housing is coupled to said outer casing of the leading one of said battery modules to permit the thermal management liquid in said inner chamber to be introduced into said accommodation space of the leading one of said battery modules; andwherein said first connection bar unit has a plurality of first connection bars, and said management module includes a plurality of said sensing units disposed in said accommodation spaces of said battery modules, respectively, each of said sensing units includinga printed circuit board disposed in said respective accommodation space,a connectivity sensor which is mounted on said printed circuit board, and which is electrically connected to two of said first connection bars of said respective battery module for detecting an electrical resistance between said two of said first connection bars,a flow meter mounted on said printed circuit board for detecting a flow rate of the thermal management liquid inside said respective accommodation space,a pressure sensor mounted on said printed circuit board for detecting liquid pressure of the thermal management fluid liquid inside said respective accommodation space, anda temperature sensor mounted on said printed circuit board for detecting temperature of the thermal management liquid inside said respective accommodation space.6. The battery system according to claim 5, wherein each of said sensing units further includes a wireless transmitter which is mounted on said printed circuit board for transmitting data collected by said connectivity sensor, said flow meter, said pressure sensor, and said temperature sensor; andsaid management module further includes a wireless receptor mounted on said management circuit board for receiving the data from said wireless transmitters of said sensing units.7. The battery system according to claim 5, wherein said pressure sensor is an atmospheric MEMS sensor.8. The battery system according to claim 5, wherein a circuit on said printed circuit board is electrically connected to a circuit on said management circuit board so as to permit data collected by said connectivity sensor, said flow meter, said pressure sensor, and said temperature sensor to be transmitted to said management circuit board.