It isn't always possible to be near an outlet to keep a charger running. A laptop is supposed to be portable. But a user may still need to be on their computer more than just 2 or 3 hours their batteries allow them. That can turn into a real problem if the person can't keep their computer running because kobalt minen its battery just died.
So from the points I have raised above we can see that we no longer need to condition the battery in the way we did with the older Ni-MH cells. Having said all of that you should always check your lithium facts manual for battery advice and especially initial charge times.
The last thing to start tinkering on is the rate of fire. The biggest thing that will determine your ROF is the battery voltage and the amount Milliampere-Hour rating (mAH). Some of the best batteries for increasing ROF are the LiPoly batteries (Lithium Polymer) but you should not use these types on out of the box guns. When preparing to use the Lipoly battery you need to make your internal components are reinforced and upgraded where they need to be.
Also keep in mind that when your iPod mini battery does die, it requires a proper funeral inside a proper container. No you don't need to buy a casket and a plot but you do need to adhere to local lithium bettery stock laws when it comes to battery disposal.
Briefly relating back to overall size... many lithium 18650's will differ ever so slightly in length (measured in millimeters). This is mainly due to an added protection circuit. The circuit helps to prevent the battery from over-discharging, since Li-ion cells can easily become damaged if their power is drained below a particular voltage. The protection circuit also prevents the cell from being over-CHARGED as well. These cells are very sensitive. They must be handled carefully, gently, and as described above, must never run-down too far, or be charged over and above their threshold. They can actually explode if severely mistreated!
The thing to realize about any battery is it does have a measurable lifespan and efforts to extend it will help but not stop the eventual demise. So the number one thing that you can do to extend the life of any of the newer lithium batteries is always take it out if you are running on DC power to lessen the heat impact. Whenever buying any replacement battery, always check the manufacture date and try to find the newest one available.