If using a clamp-on ammeter, clamp the meter around the negative wire leading from your battery. Then turn each device on and measure the change in amperage as each device is turned on and off. Similarly, with a battery monitor, simply turn the devices on/off and watch the change in current (amps) on the battery meter for each device.
The voltage across the battery terminals therefore drops from the nominal value V to (V - Ir) when a current is flowing in the circuit. In a circuit diagram we represent the internal resistance of the battery by a resistor r connected in series with the emf. A voltmeter is a device used to measure voltages, while an ammeter measures currents.
To determine the amps that each device uses you can either use a clamp-on ammeter or a battery monitor. If using a clamp-on ammeter, clamp the meter around the negative wire leading from your battery. Then turn each device on and measure the change in amperage as each device is turned on and off.
It clearly follows that the function of an ammeter is to measure that current within an electrical circuit. Ammeters measure current in two metrics - ‘draw’, the flow of current in a particular circuit, and ‘continuity’, the steadiness of the current and the presence or absence of interruptions.
To estimate battery capacity using a multimeter, follow these steps: Measure the OCV using the multimeter’s voltage setting. Compare the measured voltage with the manufacturer’s voltage vs. state of charge (SOC) chart. Estimate the battery capacity by multiplying the rated capacity by the SOC percentage obtained from the chart.
An ammeter, must be placed in series with a resistor to measure the current through the resistor. On a circuit diagram, an ammeter is shown as an A in a circle. The ammeter acts as a resistor. To prevent the ammeter from changing the current in the circuit, the ammeter must have a very small resistance compared to the resistance R of the circuit.