Every new battery need to be charged for 12 hours for initial use.
Please also perform 6 full charge/discharge cycle to ensure battery optimal performance.
If above steps are not done as shown on instruction, it may cause negative performance results.
We also recommend to check if there is any background app ia draining the phone's power. If possible, perform a factory reset on your phone to see if situation improves.
Here is a XDA forum thread explaining why the battery percentage on the phone falls rather quickly sometimes and how to resolve this problem.
If the problem still exists, we are happy to offer you a warranty replacement.