If you only have 3 volts on the wire to the meter, what would you expect to see on the meter? The meter can only read what is coming to it. 3 volts is not enough to make it read.
How do you know that the batteries are charging? Have you tested them? How? Have you charged them up? I would take the batters out, and load test them. If you do not have the test equipment to do that, take them to someone who can. Then you KNOW the batteries are good. Then install them, start the set up and see what you read on the charging circuit. On start up. A few min later.
Also, please change your location to the state you live in. Thanks.