BlackBerry Bold 9000, 9700, 9780 Replacement Battery by Lenmar

Not sure if the battery was defective or if they are slightly different than OEM. I tried to get an OEM but AT&T stores in my area out of stock. Radio Shack carried Lenmar so I bought battery from Amazon. Upon putting in, phone would reboot 3 - 6 times per day. I read on-line to put a strip of black tape on battery and this helped, would reboot 1 - 2 times per day. AT&T store got OEM (for Blackberry Bold 9000) in stock after using Lenmar for a few days so I bought and phone worked fine, no more reboots, so I concluded Lenmar was defective. OEM even seems to have much longer battery duration as well. Again, not sure batteries are bad from Lenmar or I just got a defective battery.