When the voltage across a battery is measured using a $d.c$. potentiometer, the reading shows $1.08\;V$. But when the same voltage is measured using a Permanent Magnet Moving Coil $(PMMC)$ voltmeter, the voltmeter reading shows $0.99\;V$. If the resistance of the voltmeter is $1100\;\Omega$, the internal resistance of the battery, in $\Omega$, is _________________.