Where's the money in this scheme?

First a bit of background. En has a new bike and I moved my bike computer (Garmin Edge 305) to her bike. My bike (older) has a new computer to replace it (Garmin Edge 800 -- more on that in another post).Problem: in the five years since I purchased the old computer the battery has degraded. What started off as an 8-10 hour battery life is now closer to 4 hours. Not just that but the self-discharge rate has gone through the roof (25% in three days! Gaaahh!!).Not to fear, the internet comes to the rescue with instructions on how to replace the non-replaceable battery! Internet: +1.Step one: acquire battery.This is the point of this. The battery was purchased on eBay for the princely sum of $3.05 shipped to my doorstep.How on earth is that profitable?The price of shipping is $0.44.Oddly, the USPS shipping label is printed on UPS label stock. I'm guessing that was a "donation" from UPS so I'm not going to count that (or the printer that was used to print it). The envelope is a pretty decent one with bubble padding and all that. The price I'm seeing for that is around a dime. The PayPal fee for this small transaction is $0.39.Summed up this is $0.93. This is just simple overhead that can't be avoided at any cost.The rest of this $2.12 has to pay for the product and handling.Even if the battery were free to them how is this profitable?