The battery pack includes a first battery, a second battery and a means to allow switching between the first battery and {HEAD ~ the second battery} for powering {TAIL ~ the cell phone} 
The battery pack includes a first battery , a second battery and a means to allow switching between the first battery and { HEAD ~ the second battery } for powering { TAIL ~ the cell phone }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL