I also had the new problem of rebooting and unchanging battery charge levels after battery replacement, (although greatly improved battery life), the problems were fixed with installation of a second battery. My 5S battery has 3 terminals, call them ABC. I had ~4VDC from A to C, but A to B or B to C were 0V, and infinite ohms (using either polarity, note that measuring resistance on a potentially energized circuit is only meaningful if it's actually an open circuit as was mine). The 3 conductor flat ribbon cable goes to a tiny circuit board on the battery cap, likely something was wrong there as the 3pin flat ribbon connection to main board connector was good. My good battery measured a few volts A to B (about half the voltage of A to C), but it should not read an open circuit as the bad one did.