My confidence in the dealership mechanic, as described here, is low. If indeed he suggested replacing the regulator as an attempted fix on a machine that has a topped up battery and 'will not start' then that quite unrelated action smacks of 'throwing parts at the problem and hoping for success.'
In an earlier post you said there's no spark because 'the motor is not turning over'.
That should be easy to track down, giving consideration to the difficult access to components these things often present.
Does it click or is it silent when you try to start it? Have you loosened moved and re-tightened all the big-wire connections? Don't go by, "It's OK, it's tight" there can be poor connections that still seem tight. Move em.
Use an ohm meter and check the started motor for continuity. Ohms scale, a low one. Zero ohms is dead.