Computer is slow after Replacing battery

I got a replacement battery from ifixit since asus wasn't stocking their own. the part number is b31n1637. The Ifixit battery was double the price of generic replacements. I got a friend to bring it over from the USA to Pakistan where i live. I replaced the battery and noticed immediately that the laptop had slowed down drastically and i could hear loud coil whine which was very difficult to notice before. Even the mouse cursor was lagging. I went into resource monitor and ran a cpu stress test. the maximum cpu frequency didn't go over 30%. It still went to 100% when plugged in. I double checked advanced power plans and it was at full performance. I reinstalled a fresh windows. still had the same problem. i put in the old battery and now it works fine. Is this a problem with the battery or does ASUS engage in some trickery to prevent replacements.