Disappointing battery 1

Strange behavior during 1st uses very fast discharge until the mini autonomy witness then held in time almost as long !?
After 2 months of use, the battery charged in the late evening, cell discharges at night even with off all energy-consuming functions.
Capacity announced at 1900mAh, not even equivalent to the original Galaxy S2 battery (1650mAh).
In doubt I'll ask a service but I am very disappointed by this.