Upon discharge the lead dioxide is reduced to lead oxide and {HEAD ~ the metal} is oxidized to {TAIL ~ an oxide} 
is oxidized to
Upon discharge the lead dioxide is reduced to lead oxide and { HEAD ~ the metal } is oxidized to { TAIL ~ an oxide }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL