Question on battery voltage measurement

Moin! When I use the China Cracker to measure the battery, I have the stand 11.9 volts. If I use the multimeter, I get 12.7 V. When I measure the idling speed with the China Cracker, I have 13.2 V, with multimeter 14.0 V. For all consumers and idling speed, the OBD 12.0 V ,the Multi 13.6 V shows. If the speed is up to 3000 rpm, the display does not change, with both. Is this normal that the OBD shows less and less than when I measure directly at the battery? I have a Bosch Lima installed.Now I wanted to install a new controller. Are all of them the same from Bosch? Or do I have to expand the Lima now and look at which number is on it? Because that’s how you can’t recognize anything, you have tried it with a mirror, nothing to see. Thanks already.