I'd really suspect that your converter has died. You could pull it out and see if the lightning somehow caused the reverse polarity fuses to open, but that would be a little odd. Disconnect the negative lead from the battery. Plug into shore power and use your DVM to measure DC voltage from the negative battery lead to the positive battery lead. If you have the proper voltage, the converter is likely good, and the battery is completely discharged. But once again, I highly suspect your converter is not working because the lights are dim when you are on shore power.