Your delivery time is "faster than a speeding bullet"
5 - 30 minutos
The old battery would not hold a charge for more than three hours.
I ordered two batteries prior to ordering from you. I thought I had a hand-me-down iPhone 4S. So, I ordered them and found the connectors to be wrong. I found your website which had a place to enter the serial number. That's when I found out I needed a battery for an iPhone 4. The repair took about 10 minutes with the correct battery.
The reason for my title: I ordered on Saturday, received an email (while at work) on the following Tuesday that my order was shipped. To my surprise, the battery was in my mailbox the same day you said it was shipped!
I paid for second day delivery (more than the cost of battery) for the other batteries (not from ifixit) and took over seven days in total including actually shipping and then mailing. Yours took two business days with normal mail.