Lithium-ion battery Life Span

• Lithium ion chemistry prefers partial discharge to deep discharge, so it's best to avoid taking the battery all the way down to zero. Since lithium-ion chemistry does not have a "memory", you do not harm the battery pack with a partial discharge. If the voltage of a lithium-ion cell drops below a certain level, it's ruined.
• Avoid heat, which degrades the batteries.
• Lithium-ion batteries age. They only last two to three years, even if they are sitting on a shelf unused. So do not "avoid using" the battery with the thought that the battery pack will last five years. It won't. Also, if you are buying a new battery pack, you want to make sure it really is new. If it has been sitting on a shelf in the store for a year, it won't last very long. Manufacturing dates are important.

Lithium-ion Batteries explosion

Now that we know how to keep lithium-ion batteries working longer, let's look at why they can explode. If the battery gets hot enough to ignite the electrolyte, you are going to get a fire.

When a fire like this happens, it is usually caused by an internal short in the battery. From previous article, lithium-ion cells contain a separator sheet that keeps the positive and negative electrodes apart. If that sheet gets punctured and the electrodes touch, the battery heats up very quickly. You may have experienced the kind of heat a battery can produce if you have ever put a normal 9-volt battery in your pocket. It a coin shorts across the two terminals, the battery gets quite hot.

In a separator failure, that same kind of short happens inside the lithium-ion battery. Since lithium-ion batteries are so energetic, they get very hot. The heat causes the battery to vent the organic solvent used as an electrolyte, and the heat (or a nearby spark) can light it. Once that happens inside one of the cells, the heat of the fire cascades to the other cells and the whole pack goes up in flames.

It is important to note that fires are very rare.

Source:

• Howstuffworks.com http://electronics.howstuffworks.com/lithium-ion-battery3.htm
• "Energy Density." Everything2.com http://everything2.com/index.pl?node=energy%20density
• "How to prolong lithium-based batteries." Battery University. http://www.batteryuniversity.com/parttwo-34.htm
• "Lithium-ion Rechargeable Batteries." GPBatteries. http://www.gpbatteries.com/pdf/Lithium_Rechargeable.pdf
• Needbattery.com http://www.needbattery.com/articles