At the primary power rate, {HEAD ~ a battery} may have {TAIL ~ a life} of, for example, two hours 
have
At the primary power rate , { HEAD ~ a battery } may have { TAIL ~ a life } of , for example , two hours
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH