Alex, that is reference designator U7000 and it is your "battery charger". The proper description is ISL6259 in a TQFN package and it is Intersils integrated battery charger controller for Li-Ion/Li-Ion polymer batteries. Amazingly enough it is not stocked at Mouser.com or Digikey.com, but it is available at places like this. It can be replaced, if one posses the right skills and the right tools but "Due to the excellent thermal characteristics of this mounting package, it is very hard to rework the device, as hot air reflow typically does not offer enough heat to the thermal pad without damage to surrounding board material or parts. Oxidation of the exposed chip contact pads after being exposed to a reflow oven during initial assembly makes solder wetting to them during rework quite difficult. Additionally there is no clearance for a soldering pencil to reflow pads under the chip if touch up is desired." from here. Hope this helps, good luck.