Did I maybe get a knock off battery?

[Canaan]

I ordered a replacement battery for my Macbook Pro (vintage mid 2009) and was curious as to why the charge capacity is only 4558 mAh. I tried to verify that I was ordering the correct model but of course there is always the possibility of receiving a fake so I thought I'd run it by you guys here.

Here it is.
http://www.amazon.com/LB1-High-Performance-661-5557-Notebook/dp/B004RS12X0/ref=cm_cr_pr_pb_t
The gentleman at the apple store told me to be certain it had the model number 661-5557 which this does. Could it be a matter of simply needing to calibrate it? Or maybe it's a dud. I just don't want to have it explode on me really.

Here is from the battery information:

Model Information:
Serial Number: W000101Y7784C
Manufacturer: SMP
Device Name: bq20z451
Pack Lot Code: 0
PCB Lot Code: 0
Firmware Version: 103
Hardware Revision: 000a
Cell Revision: 130
Charge Information:
Charge Remaining (mAh): 1291
Fully Charged: No
Charging: No
Full Charge Capacity (mAh): 4558
Health Information:
Cycle Count: 6
Condition: Normal
Battery Installed: Yes
Amperage (mA): -1600
Voltage (mV): 10947

Thanks to anyone who answers.