The current sensor chips: ACS712ELC-05B. Pin 5V power supply, on-board power indicator. The module can measure the positive and negative 5 amps, corresponding to the analog output 185mV/A.
Pay attention to the polarity at the load end of the device. The output will raise or fall from 2.5 volt offset.
The output would be scaled to the current drawn through power source. If this were a 5 Amp module and the power source pulled 1 Amp, the output of the module would be 2.685 volts. Now imagine the battery polarity reversed. Using the same 5A module, the output would be 2.315 volts.
IMPORTANT NOTE – This device is a Hall Effect transducer. It should not be used near significant magnetic fields.