Why does my device periodically beep twice?

This is due to overloading or underpowering. Overloading is caused by an excessive load and can be resolved by either upgrading to larger power inverter or by reducing the load of the attached equipment. If the device is underpowered, connect it to power source that is outputting greater than 11 volts. Most often, users simply need to start their vehicle and recharge the battery.