First: with the engine on, and no charging, no decent mechanic would suggest to replace the battery. I would check the alternator, probably someplace else. With the engine running remove the battery, if the engine stops there is no charge. Also, if his software shows 14 something volts and on your multimeter 11.9, and if the software is right, it means the leads from the alternator to the battery are damaged. Check with your multimeter, at the alternator( there is a 13mm nut at the side/top) and against the body of the car, see what reading you get. For the resistor to check it's value, please look at the link below https://www.google.co.uk/search?q=resistor+colour+code+chart&oq=resistor+code+colour&aqs=chrome.1.69i57j0l3.5802j0j7&sourceid=chrome-mobile&ie=UTF-8#imgrc=fKPKoho7ClunYM: I never done the so called "buttonmod", where you got the info should specify what size you need. Hope it helps.