You're making some category errors in the question. Energy can't be converted into mass, mass is a form that energy can take. In other words, when energy is "converted" into mass it never stops being energy. It's kind of like if I have a mass on a spring hanging vertically in a gravitational field, and I make it start bouncing. The energy moves back and forth from kinetic energy to the gravitational and spring stretch potential energies, and back. At no point in this process do any of these quantities not qualify as "energy". Mass, likewise, is just another way energy can be stored. If you study quantum field theory, you'll even learn that mass is one of the types of potential energies a field can store.
Charge, on the other hand, is about how a particle couples to a force. That gravity couples to mass is simply an observational fact that didn't, necessarily, have to be the case. When that distinction is being made physicists will refer to gravitational mass versus inertial mass. One of the strongest arguments for general relativity is the observed fact that gravity doesn't just couple to mass, it couples directly to energy/momentum in a way that is consistent with Einstein's equations. See: the gravitational lensing (observed many times by gravity from galaxies, galaxy clusters, microlensing, and even stars near the sun during a solar eclipse), gravitational redshift (observed frequency shift of light directed upward), etc.
Charge, on the other hand, is how various fermion fields, like the electron, up, and down fields, couple to the electro-magnetic field.
Note that total energy is conserved, so that which the gravitational field couples to is just as conserved as electric charge.