The relationship between the voltage and the current in the circuit is:
[tex]\Delta V = RI[/tex]
where [tex]\Delta V[/tex] is the voltage difference, R the resistance of the circuit (and therefore, the resistance of the battery) and I the current flowing in the circuit. By using I=19 A and [tex]\Delta V = 18 V[/tex], we can find the internal resistance of the battery:
[tex]R= \frac{\Delta V}{I}= \frac{18 V}{19 A}=0.95 \Omega [/tex]
