Keep your laptop powered on the go with this Dell Power Companion 451BBSQ portable charger, which features 2 USB ports to also charge up to 2 mobile devices simultaneously. A 5-segment LED indicator lets you know how much power is left.
Couldn't find any list of compatible laptops. Not enough Watts for XPS 15. The laptop needs 130W external charger. It may slow down battery drain of laptop when not plugged in, but not convinced it helps that much.