Patent ID: 7746031

Claim:
A monitoring device for a power supply system including a secondary battery, a load receiving power supply from said secondary battery, and a relay arranged between said secondary battery and said load, said monitoring device comprising: a sensor for measuring a quantity of state of said secondary battery; a battery monitoring unit supplied with an operating supply voltage common to said sensor and operating to monitor a state of said secondary battery; first sensing means for sensing that a measurement value obtained by said sensor falls outside a prescribed normal range in a state before connection of said relay; second sensing means for sensing that said operating supply voltage is below a prescribed operation guaranteed value of said battery monitoring unit; and abnormality sensing means for sensing an abnormality of said battery monitoring unit when said first sensing means senses that the measurement value obtained by said sensor falls outside said normal range before connection of said relay and when said second sensing means senses that said operating supply voltage is below said operation guaranteed value.