If your batteries are good and you show no power I would follow the positive wire off the battery to the first resettable fuse. Then test to see if you are getting power off both sides of the fuse. Sometimes these fuses fail there may be 2 of them next to each other. if that is not the problem them you will have to try to follow the positive side with your tester and check to where the problem is. Hopefully it is not your inverter.