Detecting an end of life for a battery using a difference between an unloaded battery voltage and a loaded battery voltage

A method for detecting the end of the life of a battery of an electronic device comprising:

• sampling a voltage of a battery while the battery is unloaded using a sample and hold circuit that comprises:
• 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, and a source terminal, wherein the base terminal and the source terminal are electrically connected to a first node that is electrically connected to a battery and the drain terminal is electrically connected to the second node;
• storing the sampled unloaded battery voltage using the capacitor in the sample and hold circuit;
• measuring a voltage of the battery while a load is applied to the battery;
• calculating a difference between the sampled unloaded battery voltage and the measured loaded battery voltage;
• amplifying the calculated difference using a differential amplifier circuit;
• and
• comparing the amplified difference to a predetermined value to detect the end of the life of the battery.

A system for detecting the end of the life of a battery of an electronic device comprising:

• a sample and hold circuit configured to sample the unloaded voltage of a battery, 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, and a source terminal, wherein the base terminal and the source terminal are electrically connected to a first node that is electrically connected to a battery and the drain terminal is electrically connected to the second node;
• a differential amplifier circuit configured to receive the sampled unloaded battery voltage from the sample and hold circuit and calculate and amplify a difference between the sampled unloaded battery voltage and a loaded battery voltage;
• and
• a microcontroller configured to receive the amplified difference from the differential amplifier and compare the amplified difference with a predetermined threshold value.