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