The unit is a bit of a challenge to get the batter in place as the contact pins are adjustable and move around. Concerned that they might break off. Charges batteries quickly and light changes from red to blue as the charge progresses. Instructions indictae that you can charge a device (phone) using the USB port on the side from the battery installed in the charger. I cant get it to work, will not charge any of 4 phones I have tried using 3 different cables. Need to decide if defective or incorrectly advertised. Batteries last longer in phone than OEM.

Update - seller contacted to address my question/concern. The unit will charge a phone through the USB port only while plugged into an external power source. I had understood (incorrectly)that it would also charge the phone from a charged battery that was in the charger.