 Features of lithium Ion batteries  High energy density that reaches 400 Wh/L (volumetric energy density) or 160Wh/Kg (mass energy density).
 High voltage. Nominal voltage of 3,6V or even 3,7V on newer Li-Ion batteries.
 No memory effect. Can be charged any time, but they are not as durable as NiMH and NiCd batteries.
 High charge currents (0,5-1A) that lead to small charging times (around 2-4 hours).
 Flat discharge voltage allowing the device to stable power throughout the discharge period.
 Typical charging Voltage 4,2 ± 0,05V.
 Charging method: constant current - constant voltage (CV-CC).
 Typical operation voltage 2,8V to 4,2V
 Recommended temperature range 0-40
 Charging Characteristics Charging method is constant current - constant voltage (CV-CC). This means charging with constant current until the 4.2V are reached by the cell (or 4,2V x the number of cells connected in series) and continuing with constant voltage until the current drops to zero. The charge time depends on the charge level of the battery and varies from 2-4 hours for full charge. Also Li-Ion cannot fast charge as this will increase their temperature above limits. Charging time increases at lower temperatures. 
Typical charging characteristic
Charge current is recommended to be set at 0,7CmA (where C is battery capacity). If voltage is below 2,9V per cell it's recommended to charge at 0,1CmA. Charging environment must have a temperature between 0-40 . Maximum discharge current must not exceeds 1.0CmA and discharge voltage must not go below 3,0V  Capacity
At a typical 100% charge level at 25 , Li-ion batteries irreversibly lose approximately 20% capacity per year from the time they are manufactured, even when unused. (6% at 0 , 20% at 25 , 35% at 40 ). When stored at 40% charge level, these figures are reduced to 2%, 4%, 15% at 0 , 25 and 40 respectively. Every deep discharge cycle decreases their capacity also. 
Typical capacity characteristic over charge cycles
100 cycles leave the battery with about 75% to 85% of the original capacity. When used in notebook computers or cellular phones, this rate of deterioration means that after three to five years the battery will have capacities too low to be still usable.  | Tip: To increase battery life store it at 40% level at low temperatures (even to the refrigerator but not below 0 degrees Celsius) and never discharge it full. Charge it early and often. Excess heat can damage the battery. Also charge once a year to prevent overdischarge. |
 Self discharge
One great advantage of Li-Ion batteries is their low self-discharge rate of only approximately 5% per month, compared with over 30% per month and 20% per month in nickel metal hydride batteries and nickel cadmium batteries respectively. | Chemistry Type | Ni-Cd | Ni-MH | Lead acid | Li-ion Cylindrical | Li-ion Prismatic | Li-Po | Nominal Voltage (V) | 1.2 | 1.2 | 2,1 | 3.6 | 3.6 / 3.7 | 3.6 | Specific Energy (Wh/Kg) | 50 | 70 | 30 | 80 | 100-160 | 140 | Specific Energy (Wh/L) | 150 | 200 | - | - | 250-360 | - | Cycle Life (Times) | 500 | 560 | - | 1000 | 1000 | - | Environmental hazard | low | medium | medium | high | high | high | Safety | High | High | medium | low | low | low | Cost | low | medium | low | high | high | high | Self-Discharge Rate (%/month) | 25-30 | 30-35 | - | 6-9 | 6-9 | - | Memory Effect | yes | yes | yes | no | no | no |
Comparison table of the most common batteries types  Precautions
Be sure to follow the safety rules listed below (PANASONIC recommendations):
• Do not place the battery in fire or heat the battery.
• Do not install the battery backwards so that the polarity is reversed.
• Do not connect the positive terminal and the negative terminal of the battery to each other with any metal object.
• Do not carry or store the batteries together with necklaces, hairpins, or other metal objects.
• Do not pierce the battery with nails, strike the battery with a hammer, step on the battery, or otherwise
subject it to strong impacts or shocks.
• Do not solder directly onto the battery.
• Do not expose the battery to water or salt water, or allow the battery to get wet.
• Do not disassemble or modify the battery. The battery contains safety and protection devices which, if damaged, may cause the battery to generate heat, rupture or ignite.
• Do not place the battery on or near fires, stoves, or other high-temperature locations. Do not place the battery in direct sunshine, or use or store the battery inside cars in hot weather. Doing so may cause the battery to generate heat, rupture, or ignite. Using the battery in this manner may also result in a loss of performance and a shortened life expectancy 
| Use common sense precautions. Do not short circuit, overcharge, crush, mutilate, nail penetrate, incinerate, reverse polarity, heat above 100 degrees Celsius, solder directly on the metal can. Dispose them following local batteries disposal rules. |
 Safety circuits inside a Li-Ion battery pack Inside a Li-Ion pack there is always a safety circuit that consists of four main sections: 1. The controller IC that monitors each cell (or parallel cells) voltage and prevents the cells to overcharge or overdischarge controlling accordingly the cutoff switches. Also the voltage across the switches is monitors in order to prevent over current.
2. The control switches that usually comprises FET structures that cutoff the charge or discharge depending on the control signals of the controller IC.
3. The temperature fuse that cutoff the current if the control switches experience abnormal heating. This fuse is not recoverable.
4. The thermistor (usually PTC) that measure the battery temperature inside the pack. It's terminals are connected to the charger so it can sense the temperature of the pack and control the charge current until the battery it's full charged. 
A typical structure of Li-Ion battery pack (block diagramm)
| Battery packs made from Li-Ion cells always have protective circuits and PTC elements to monitor battery status any time. Never remove this circuitry as this will cause ignition. |
Now you have read and understand all the above information you see that charging a Li-Ion pack can't be done with simple charge methods used in other type of batteries. So never charge a Li-Ion cell if you are not completely sure what you do. Now it's time to continue to the step by step guide to see how we can safely reconstruct a Li-Ion pack.
How to rebuild a Li-Ion battery packHow to rebuild a Li-IonbatterypackHow to rebuild a Li-Ion battery packHow to rebuild aLi-Ionbattery packHow to rebuild a Li-Ion batterypack
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