Using an iMax 6 hobby charger, you can discharge and re-charge the 18650 cells (and mostly anything else that's rechargeable). The display reads out the current in mah used to charge/discharge. It's useful to identify how much current any battery can store. I used them to recover all the 18650's from bad laptop batteries. I also bought some budget 18650's online just to compare. The iMax charger cost like $15 on eBay.
The budget new 18650's seemed to discharge about 300 - 450 mah and rarely found one that went close to 700 mah. None of them seemed to be equal to each other. The laptop batteries worked alot better getting over 1,000 mah on many of them.
Due to the cost of real 18650 batteries and the chances I would get ripped off, I never bought the new real certified ones, so I can't provide any statistics on comparing to good grade batteries. The junk/recycled ones I have used work perfect for flashlights and I use them for Arduino testing.
There are alot of statistics involved with batteries regarding their lifetime, and the amount of current that can be passed at a given time. Some batteries will discharge alot right away and allow themselves to be drained down rapidly - like if you wanted to use them to turbo-boost sprinting on an e-bike. Other batteries will only discharge lower current, slowly - they shut down if too much current draw at one time - like when your power drill suddenly stops, but in 10 minutes you can use it again for small bursts. Anyone can probably spend weeks reading all the details on the different grades and types of 18650 batteries. In order to know what you have, you have to buy makes and models of certified ones from known distributors, which cost a whole lot more then just taking a random chance with cheap or recycled batteries.