I hope you have your new 12V batteries connected in a parallel configuration and not in series. You may wish to check your connections and make sure that they are connected correctly. Also check that all connections are tight and clean.
I know you had questions in another thread about which wires were to connect to others so there may be some miswiring going on. If that happened, there may be fuses blown or circuit breakers tripped. I would check them all especially what ever is protecting the wire from the battery to the converter. That circuit breaker or fuse should be close to the batteries.
Another thing would be the connection to ground. If that wire was loosened while you were changing batteries or if the ground connection to frame is corroded, you won't have good charging either.
