Well battery fitted and power system calibrated. My battery count shows 6. So it would appear the battery counter is working. The battery "service" icon has disappeared as well. So it cost me £25.99 for the battery. The pack also included 2 tools. 1 for removing the screws on the back of the laptop. (I already had this). Another tri-wing for getting the 2 screws that retain the battery. (this I didn't have)
Care was required when reinstalling the 2 tri-wing screws. The hole pitch on the battery was ever so slightly out and it took a few attempts to get them in correctly. The thread is delicate and probably around 1.5mm. So the chances of cross threading are high.
It took me about 15 mins to fit the battery. If you are so minded you could omit the power calibration part and just operate it as you normally do. All the information I had said you needed to power calibrate on this model. First step is to fully charge and give it an extra 2hrs. 2nd part is to run it down and then leave it 5hours beyond its shut down point. Then fully charge again.
If you do a battery replacement I recommend a clean soft working surface. A way to identify which screws go where. There are different lengths. As for static I just ground myself out on the cold water system just before I started the job. I don't know if it helps but it was the best solution I had.
The battery was the original fitted by apple, so 6 years is not to shabby. I have had this machine for about 1 year. Bought off this site and very pleased with it. I removed the HDD and fitted a Samsung SDD, big difference and highly recommended.