Load tester vs Multimeter

I'm testing old 12v batteries. I'm using a load tester and a multimedia. I'm confused as to why the load tester is measuring a different voltage than the multimeter. Without any load on it. Is on one battery for instance the multimeter reads 12.83. And the Is load tester reads 6v. I'm completely new to this and any advice would be much appreciated.
 
I'm testing old 12v batteries. I'm using a load tester and a multimedia. I'm confused as to why the load tester is measuring a different voltage than the multimeter. Without any load on it. Is on one battery for instance the multimeter reads 12.83. And the Is load tester reads 6v. I'm completely new to this and any advice would be much appreciated.
Load tester measures the battery voltage under given load conditions, so the measured voltage is a EMF - Rint*Iload=EMF - Rint*EMF/(Rint+Rload). The voltmeter measures the unloaded battery voltage = approximately EMF (the voltmeter input resistance Rint is very high).
 
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