AWESOME. It was really 10 minute repair. Easy to take the cover off, and it was easy to take the battery out. The battery temperature is at 25 degC. The only hard part was slipping the cover back on.
I watched the ifixit videos, read the instructions, and most importantly I read what the people said after replacing the battery. I found out there are three reasons why the home repairs go wrong. (1) The first is not keeping track of the screws. They are of different lengths, and putting a long screw where it does not belong will ruin the motherboard. Mark them with colored sharpies. (2) The second is not being able to remove the tape that is holding the battery. Use the heat gun!!! I broke the second tape even with the heat gun, and I had to use a credit card to pry it out. (3) The last one is not insulating the battery connector. A metal battery bracket (Step 15) goes over the battery connector, and it will short the battery. Put an electric tape over the battery connector. I think the third reason is why the phone starts acting crazy.