New Battery, 91% after 6 charges. Problem?

I've just replaced the battery in my 2010 Macbook Pro on Mountain Lion. After six charges, battery health is only showing 91%. I've had it less than a week and it's dropping around one percent each day. Is this normal? Will the battery health stablize or do I have a problem?

Thanks

PS The old battery lasted 2 1/2 years and 1100 charge cycles. In sept, when I installed ML, the battery was still showing 87% battery health after a 1000 cycles. After two months on ML the health dropped to 80% and then the battery failed.