Battery Charger Earthing

I have a C-Tek intelligent charger which I have used for a number of years. However, I went to take off the tow hitch whilst the charger was on and discovered that there was a charge through the spanner I was using. Guess I was earthing the system but is this normal as I have had no issues with the charger or the batteries? Doubt it will fry the wiring but just want to check with the experts out there.

Thanks,

Joe