There is no formula!
You need to get the battery voltage settings for the injectors from the manufacture of the injectors, most can be found on line just search.
As for the Krkte, just pick a value which you think it close the actual, probably based on the formula stated below and then do some logging, if the ecu is adding fuel then increase the krkte and if its taking fuel off then decrease it.... until the fuel trims are as close to 0 as you can be bothered. you have a 25% +/- to work with.
I just saw for voltage to the battery on the internet
thank you very much I will test it and I will feedback