Each of {HEAD ~ the casings} includes a coverable opening through which the electrolyte solution within {TAIL ~ the cell} is replaceable 
Each of { HEAD ~ the casings } includes a coverable opening through which the electrolyte solution within { TAIL ~ the cell } is replaceable
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH