C-Tek 4.3. Think they might have a new one 5.0. If you get the 4.3 when you first start it scroll the mode button so the light goes to the snow flake. That will kick it up to 4.7. I did modify the power plug in the rear compartment to be live all the time. Just ran a wire (positive ) from the outlet directly to the battery. Easy to do. That way the outlet is always connected and you can leave the charger hooked up as long as you want. Once its fully charged it goes into maintain mode. These batteries are GSM and charge slow. New technology . If I am not going to drive mine for a few days I just hook it up . Easy to do.