You charged the batteries, are the connections tight?
Did you remove the battery connection to charge the batteries?
Did you TEST the batteries? Load test them?
Remove the connections, and test each battery separately.
Are they the batteries that came with the set? Are they new?
What readings do you get?
Flickering lights could mean bad/loose connections, or low battery voltage. And no, when the batteries are low, its not going to start. I have 4 batteries out in the garage, that I charged, and they read 12.2 volts. None of them are good. Load test the batteries if they are not brand new.