Old battery (about 3yrs) run out very fast, only able to hold about 3 hrs per charge. Order new battery from iFixit hope that it will 6-7hrs per charge.
Battery replacement process went very smooth and easy. Just removed few screws that hold the back cover, then removed another few more that hold battery to the board.
I expect the new battery will last about 6-7hrs per charge, unfortunately it only improve a bit. It only last for about 4 hrs slightly better than my old battery which still hold about 3hrs per charge and it's 3 yrs old (969 charge cycle - 87% health).
The new battery also look like have few scratches at the back even it cover with plastic. I don't mind the scratches as long as it's new and serve the purpose.
Don't buy this if you expect it to last longer than 4 hrs.