This is a tough one to nail down, as there are many different manufacturers of chargers. I will focus on the newer style smart battery chargers. These newer fully automatic chargers need to be hooked up to a battery before they will output any voltage. This is primarily a safety feature that prevents spark when hooked up, and protects the charger against reverse polarity hookup. Some chargers need to ‘see’ as much as 5.5 volts before they recognize that they are attached to a battery. Once the charger is hooked up, it will begin putting out about 14.2-14.7 volts to a battery that needs to be charged. If your charger does not do this, you may want to contact the manufacturer for further troubleshooting tips.