The invention belongs to a control technology, and particularly relates to an estimating device and a method which are used for a battery level of a battery arranged on a special vehicle. A digital single chip central processing unit (CPU) which integrates an analog to digital (AD) interface, an integrated optics (IO) interface and a serial peripheral interface (SPI), a Twin controller area network (CAN) interface and a serial port serial control interface (SCI) as a whole is adopted, thereby facilitating the expansion of the external devices. Double CAN buses of a data communication unit are mutually used as back-ups, after errors of one of the buses occur, the other of the buses works, and therefore communication reliability of the device and an upper computer is improved. The estimating device fully considers specialties of the special vehicle, adopts a modularized design concept, and is easy to maintain, low in cost, high in reliability, and easy to operate. Power up time difference between this time and last time is calculated, an initial value of electrical quantity of a storage battery can be ensured and calculated through an interpolation checking table, and a state equation and an observation equation are rapidly built in an off-line mode. A coefficient n, determined through the interpolation checking table, of a Peukert equation and battery available capacity calculated through charge discharge efficiency eta are closer to actual using battery capacity, and estimated electric quantity of a storage battery is more precise.