Bitfields for APM v1.1+ battery flag:
Bit(s)	Description	)
 0	high
 1	low
 2	critical
 3	charging
 4	selected battery not present (APM v1.2)
 5-6	reserved (0)
 7	no system battery
Note:	all bits set (FFh) if unknown
SeeAlso: #00476,#00478