Battery Facts (Q&A):
Question
When do you charge a lithium ion battery? Do you wait until it's very low like around 20% or is it good to start charging the battery when the voltage drops? How do you maintain a good healthy lithium ion battery?
Answer
Unlike nickel-cadmium and nickel-metal hydride rechargeable batteries, lithium-ion (li-ion) rechargeable batteries have no memory effect, therefore, it is not necessary to fully discharge your battery before recharging. Actually, li-ion batteries will generally last longer if you do not completely discharge them before recharging. For example, if you regularly recharge a li-ion battery only after discharging it completely (known as "100% Depth of Discharge"), you can generally expect to obtain between 300 and 500 charge-discharge cycles. However, if you recharge the battery after only a partial discharge, e.g., 50%, you can expect to achieve over 500 charge-discharge cycles; even more if you use a lower depth of discharge, such as 20%. Therefore, you can effectively recharge li-ion batteries even if they have only been discharged for a short time.
To maintain a healthy battery, follow the device manufacturer's charging recommendations, and do not expose the battery to temperatures above 60 degrees C (140 degrees F).
Polymer Charging
Question
We plan to use constant voltage - constant current to charge a Lithium Polymer battery:
1. What is the maximum current charge allowed? 1C, 1/2C or what?
2. Can we charge a Lithium Polymer battery EXACTLY like a Lithium Ion battery?
Answer
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At 08/16/2001 10:09 AM we wrote - The maximum charge current allowed is the C Rate of the individual cell (1C). The recommended charge current is the C/2 rate (0.5C).
You can charge a Lithium Polymer battery exactly like a Lithium Ion battery providing the above charging rates are used. Please refer to our Safety Precautions Guide for detailed information on charging.
Lithium ion and polymer charging recommendations
Question
I am trying to get the correct information regarding the use of my battery in mobile phones and computers. At the store, when we buy a new phone, they suggest to fully charge the lithium-ion/Polymer battery for at least 24 hours, then discharge completely until the device powers off itself, and than repeat this operation two more times. In an article I've read, they mention that the lithium battery life would be affected if discharging completely before charging.
So, what is the best way to keep my lithium-ion/Polymer battery in the best condition so it provides good performance and lasts long?
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Answer
We recommend fully charging your battery before using it the first time. 24 hours is not necessary, as your charger and battery circuitry will automatically stop charging the battery when it's fully charged, generally in 3 to 6 hours. Unlike nickel-cadmium and nickel-metal hydride rechargeable batteries, li-ion and polymer rechargeable batteries have no memory effect, therefore, it is not necessary to fully discharge your battery before recharging.
Li-ion and polymer cells and batteries will generally last longer (more charge/discharge cycles) if you do not completely discharge them before recharging for the following reasons:
The shelf life of a lithium ion cell is a function of the self discharge, temperature and state of charge (SOC) conditions imposed upon the cell. As the storage temperature and SOC increase, the resultant capacity upon discharge decreases and the impedance of the cell increases. The shelf life is almost cut in half by holding the cell at 100% SOC at temperatures between 30C and 60C as opposed to 50% SOC at the same temperature range. The effect is not as pronounced at room temperature, with the shelf life roughly 75% at a 100% SOC condition as opposed to 50% at elevated temperatures.
Float charges can harm lithium ion chemistry and are not recommended.