The real fact about your Lithium-ion battery life and death

Nowadays, Lithium-ion battery is commonly used to power up electronic gadgets including laptop, netbook, tablet PC, mobile phone, cordless phone, digital camera, GPS navigator, PDA, MP3 player, etc.

There are quite a lot of information in the Internet teaching you how to prolong the lifespan of your Lithium-ion battery, but not all of them are true. Some are even misleading and ridiculous.

The information below is summarized from 2 websites, namely:

1. batteryuniversity.com
2. howstuffworks.com

which I believe to be more reliable source to learn about the real fact of your Lithium-ion battery life and death.

Here we go:

• Lithium-ion batteries age. They start degrading as soon as they leave the factory. They will only last 2-3 years from the date of manufacture whether you use them or not. You should fully make use of your Lithium-ion battery, because it will still die off even if you store it aside and not using it for long time.
• Lithium-ion batteries are good in holding charge. A lithium-ion battery pack loses only about 5% of its charge per month when not in use. (Compared to 20% loss per month for NiMH batteries)
• Lithium-ion batteries have no memory effect. You don't have to completely discharge them before recharging.
• If you completely discharge a lithium-ion battery, you can no longer recharge it. It is ruined. However, the battery has electronic mechanism to prevent it from complete discharge by stop working when the voltage is too low. A fully discharged battery left for a long period of time will lose its charging capacity.
• Lithium-ion batteries can handle hundreds of charge/discharge cycles. Don't worry about recharging it often.
• Lithium ion chemistry prefers partial discharge to deep discharge. Your battery can have longer life if you charge it often rather than charging it after deep discharge.
• Lithium-ion batteries can have as much as 4,700 discharge cycles if you recharge it at every 10% drop in capacity; 2,500 discharge cycles if you wait until 25% drop; 1,500 discharge cycles if you wait until 50% drop; and only 500 discharge cycles for 100% full recharge.
• Avoid leaving them in high temperature, such as in a car parked at sunny outdoor. Heat causes lithium-ion batteries to degrade much faster than they normally would. Keep your battery below 30°C (86°F). Extremely high temperature might also cause battery explosion.
• When stored in 0°C, Lithium-ion batteries suffer about 6% permanent capacity loss in 1 year. At 25°C, they suffer about 20% permanent capacity loss in 1 year. At 40°C, they suffer about 35% permanent capacity loss in 1 year. At 60°C, they suffer about 40% permanent capacity loss in 3 months.
• Normally, there is built-in mechanism to prevent Lithium-ion batteries from overcharging, so you don't have to worry about battery degrade due to overcharging. However, if such mechanism failed, overcharging might cause excessive heat generated, which is harmful to the battery's lifespan.
• Most lithium-ion batteries cannot exceed 4.20V/cell. While a higher voltage would boost up the battery's capacity, over-voltage shortens its life.
• High charge levels and elevated temperatures hasten permanent battery capacity loss. This is the reason why some people prefers to remove the battery from laptop when it is on A/C power (so that the battery will not be always fully charged, and expose to the heat generated by the laptop). 
• Storing the battery at 40%-60% state-of-charge instead of fully charged can prolong its life.
• Avoid ultra-fast charging and discharging. If the charger allows, lower the charge voltage limit to prolong battery life. In this case, sometimes charging the electronic gadget by connecting it to a computer's USB port is more preferable than charging it with wall socket charger.