No need for that!
It is not a battery tester, but only a voltmeter, which uses a battery to operate and displays the voltage.
A good battery tester should use a circuit with moderate resistance to measure the battery in a circuit with current flowing through it. Measuring a no-load voltage will only differentiate a completely discharged battery from others, new and partially used batteries will not be distinguished.
It is bigger and less beautiful, but buy this article instead: https://www.ldlc.com/fr-be/fiche/PB00273327.html