[Q] have a problem with my extended battery 5000 mAh

hey everybody
hope that you are all okay :)

i just ordered an extended battery with the capacity of 5000 mAh
here is its link
http://www.ebay.com/itm/New-5000mAh-...-/330750349616

and that was 4 days ago.
the problem is, the battery drains so fast
for example, when the phone is idle, it may use up to 12% in about 7 hours
and if i'm surfing the internet using mobile data (3g)
it may not even remains 2 hours of continuous usage
it also doesn't stay much with display on> about 3.5 hours only

while my friend who ordered with me the same battery
its battery remains much longer than me

could it be the rom i'm using or something else?

i'm on [ROM] Sweet ROM V11 LTA 4.1.2 [October 25th]