Why the dell latitude 5285 battery has 7.6V and 11.4V battery? are they fully compatible?

We don't believe they are compatible at first place, we especially checked the official manual, and it turns out it does have this 2 version and they are fully compatible, we also copied the battery information, we could check it too.

original dell latitude 5285 battery 32W

32Whr : 

Length: 177.6 mm (6.99 inches)
Width: 82.6 mm (3.25 inches)
Height: 5.5 mm (0.21 inch)
Weight: 135.0 g (0.29 lb) (126 GB m2 SATA)
Voltage: 11.4 VDC

  original dell latitude 5285 battery 42W

42 WHr:

Length: 177.6 mm (6.99 inches)
Width: 82.6 mm (3.25 inches)
Height:5.5 mm (0.21 inch)
Weight: 170 g (0.37 lb)
Voltage: 7.6 VDC

Life span 300 discharge per charge cycles