What all this means is that with the mains power on, the output voltage will be up around 13.8 to 14 volts. With the mains power off, the output voltage will gradually drop to around 10 volts as the battery goes flat. Any good equipment designed to be 12V battery powered will operate normally down to 10 volts. Security, Access Control and similar installations will also have to consider the volt-drop in long cable runs. Many door locking devices fail to operate correctly even with a small voltage reduction.
Magnetic clamps reduce holding force and solenoid based locks become unreliable or fail altogether.
These shortcomings can cause a serious lack of security that is overlooked by many system designers. The continuous output current rating is limited mainly by temperature rise in a relatively confined space. The standard unit has a small fan which moves air slowly through the interior. The additional airflow reduces the operating temperature, which makes the continuous current rating 3.5 Amps. Because fan life and reliability is an important issue, the fan is run at a slightly reduced speed and only when required.