Looking at another aspect of the architecture, the basic interconnection of charging a battery that is built into a portable device is shown here. As opposed to a battery that is removed from the device to charge, it is possible to try and operate the product/system while the DC source is connected – simultaneously charging the battery and operating the equipment. Given this, and given that the charger output, battery terminal, and system input are all connected at the same point, there can be a few limitations with this architecture. Primarily, in the case of a very deeply discharged, or even defective battery, it may not be possible to power up the system even when an external power source is connected. So, if a product has a deeply discharged battery, the end-user may think the entire system is dead when they plug in the charger and apparently nothing happens because the system cannot power up. Again, for products with removable batteries, it may be possible to remove and replace a defective battery with a different pack, but if the cell is embedded within the equipment, then a defective battery will render this entire product useless.