NOVELTY - The system (22) has a low pressure vessel (26) containing a low-pressure vessel wall that defines a low-pressure vessel cavity. A high-pressure accumulator (25) contains a high-pressure accumulator wall defining a high-pressure accumulator cavity and including an aluminum layer, where the high-pressure accumulator is placed in the low-pressure vessel cavity. A flexible bladder is placed in the high-pressure accumulator cavity. A sensor module is operably connected to the aluminum layer. A CPU is operably connected to a strain gauge of the sensor module.    USE - Integral accumulator/reservoir system i.e. tank-in-tank system, for a closed-loop braking energy regeneration system utilized with a vehicle prime mover (all claimed) of a hybrid hydraulic vehicle.    ADVANTAGE - The system relieves pressure from the high-pressure accumulator to the low pressure vessel through an emergency relief valve in response to an emergency signal during emergency condition such as vehicle crash and potential tank failure. The low-pressure vessel is made of lightweight material to maintain low mass for the system. The system includes a plastic layer increasing number of pressure cycles that the high-pressure accumulator can withstand. The plastic layer increases lifetime of the flexible bladder by providing a smooth surface that the flexible bladder can slide against the surface. The system includes a poppet valve accumulator opening whose diameter is 3 inches so as to allow the thickness bladder to be inserted into the high-pressure accumulator, thus avoiding problems with permeation of gas through the bladder and extending life of the bladder. The system includes a nonstructural fiberglass layer whose thickness is 0.01 inches, so that the fiberglass layer protects the carbon layer.    DETAILED DESCRIPTION - The sensor module comprises a global positioning system (GPS) interface and a global system for mobile communications (GSM) interface. An INDEPENDENT CLAIM is also included for a braking energy regeneration system for use with a vehicle prime mover, comprising a power transfer module.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of a braking energy regeneration system with an integral accumulator/reservoir system.    Closed-loop braking energy regeneration system (20)    Automatic control system (21)    Integral accumulator/reservoir system (22)    High-pressure accumulator (25)    Low pressure vessel (26)