IME this is only partially true. The output current seems to be limited, and to be too wimpy to both charge the battery and run the laptop - which means that in some cases I have had to remove a low battery in order to run the laptop. There seems to be some kind of over-current trip, which turns off the power for a few seconds if you try to draw too much. In some cases I have been able to get around the problem by turning the backlight right down when I have a part-discharged battery.

However, with the laptop off, I have been able to charge the laptop battery. Depending on your laptop and power supply, YMMV.