iPhone 4S shutting down 20-30 % - battery already replaced I've had my iPhone 4S for 3 years and it now runs iOS 7.1

Battery was performing badly so I decided to replace it.


I bought a spare battery online by duracell direct (average quality good!)
Replaced battery by myself (easy!)
First 2 running cycles are OK


Now, the iPhone shuts off at 30 % (sometimes at 20%). I can even reboot it and use sometines below 10 %, but experience is awful. Tried to do 2-3 calibrations but no luck.

I checked real battery status with iBackupbot, seems ok.

Here follows a log frm iBackupBot:

Info da iBackupBot il 30/12/2014
Battery

 CycleCount: 5
 DesignCapacity: 1430
 FullChargeCapacity: 1393
 Status: Success
 BatteryCurrentCapacity: 67
 BatteryIsCharging: true
 ExternalChargeCapable: true
 ExternalConnected: true
 FullyCharged: false
 GasGaugeCapability: true


Any ideas?
Few ideas:


Have you tried a full blown factory restore? 
Are you SURE everything internally on your phone is secured and exactly as it was when you first opened it? Might be worth it to open it up again and double check.
Have you contacted the battery seller? I've personally never heard of 'em, but then again I've never been in the market for a new iPhone battery. I would contact them and let them know about the issue. It very well could be that you were sent a dud. 
Last resort: Get it replaced. Not sure what would've gone wrong with the battery replacement, but there ya go. Contact your cell phone service provider or an Apple Store and see if you can either get it fixed by them or get a replacement.