Patent ID: 8410783

Claim:
A circuit for detecting the end of life of a battery of an electronic device comprising: a first node electrically connected to a battery; a load intermittently electrically connected to the first node, the load configured to be applied and removed from the circuit; a sample and hold circuit electrically connected to the first node, the sample and hold circuit configured to sample and hold an unloaded battery voltage, the sample and hold circuit comprising: a capacitor electrically connected between a second node and ground; a first operational amplifier comprising an inverting input, a non-inverting input and an output, wherein the non-inverting input is electrically connected to the second node and the output is electrically connected to the inverting input; and a field effect transistor comprising a base terminal, a drain terminal, a gate terminal and a source terminal, wherein the base terminal and the source terminal are electrically connected to the first node and the drain terminal is electrically connected to the second node; and a differential amplifier electrically connected to the sample and hold circuit, the differential amplifier configured to calculate and amplify a difference between the sampled unloaded battery voltage and a loaded battery voltage.