It's important to remember that the need to bond the aircraft to the source of the fuel (which might involve "grounding" too, but not necessarily) is because of the possibility of a latent static charge residing in the aircraft which has the "potential" to jump to the fuel source in the form of a spark. This has nothing whatever to do with the aircraft electrical system, nor household "mains". After all, we also bond aircraft which do not have an electrical system during fueling too!