NOVELTY - Battery pack comprises lithium polymer cells (110, 112, 114, 116); first order battery protection circuit coupled to at least one sensor and battery disconnect switch for disconnecting battery from power source in response to first predetermined condition; second order battery protection circuit coupled to at least one sensor for disconnecting battery from power source in response to second predetermined condition; and fluid warmer over-temperature protection circuit for disconnecting battery from power source in response to sensing excessive fluid temperature.    USE - Battery pack used for powering intravenous fluid warmer (105) used in military and civilian emergency settings, e.g. battlefield or civilian medical facility.    ADVANTAGE - The batteries can be charged while in use by internal charger. Battery charging and discharging are accomplished in controlled and protected manner to avoid overcharging and over-discharging conditions. The battery pack or battery cells are enclosed in fire and/or explosion resistant enclosure.    DETAILED DESCRIPTION - The sensor comprises temperature sensors, voltage sensor, current sensor, stress sensor, and/or strain sensor. The battery pack also comprises thermal fuse coupled to second order battery protection circuit and fluid warmer over-temperature protection circuit, such that second order battery protection circuit opens thermal fuse in response to second predetermined condition, and fluid warmer over-temperature protection circuit opens thermal fuse in response to sensing excessive fluid temperature. It further comprises battery condition indicator coupled to first order battery protection circuit and having display and/or annunciator; charger connected to lithium polymer cells to directs discharge load current on path partially separate from path of charging current; and fire and/or explosion resistant enclosure containing lithium polymer cells. Electric current output from battery pack conducts in circuit partially separate from charger. An INDEPENDENT CLAIM is included for apparatus for use with system for warming intravenous fluid to be administered to living body comprising housing, lithium polymer cells, heater, fluid warmer, battery condition indicator, first and second order battery protection circuits, and fluid warmer over-temperature protection circuit.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of fluid warmer assembly.    Fluid warmer (105)    Lithium polymer cells (110, 112, 114, 116)