2006 Honda Civic Owner's Manual - Page 227

Checking the Battery If you need to connect the battery to a charger, disconnect both cables to prevent damaging your vehicle's electrical system. Always disconnect the negative ( ) cable first, and reconnect it last. If your vehicle's battery is disconnected or goes dead, the audio system will disable itself. The next time you turn on the radio you will see ''ENTER CODE'' in the frequency display. Use the preset buttons to enter the code (see page 172 ). On vehicles with navigation system The battery gives off explosive hydrogen gas during normal operation. A spark or flame can cause the battery to explode with enough force to kill or seriously hurt you. Wear protective clothing and a face shield, or have a skilled mechanic do the battery maintenance. The navigation system will also disable itself. The next time you turn on the ignition switch, the system will require you to enter a PIN before it can be used. Refer to the navigation system manual. Maintenance 249