The power source may be interchanged between {TAIL ~ an AC powered sealed unit} and {HEAD ~ a DC powered battery pack} 
The power source may be interchanged between { TAIL ~ an AC powered sealed unit } and { HEAD ~ a DC powered battery pack }
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD