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While storing a Lithium Polymer battery cell or a device with a Lithium Polymer battery why should we make sure to discharge the battery to 40-60% (and only then put it to storage)?
What happens if you store a Lithium Polymer battery with 100% charge and WHY DOES IT HAPPEN?
I am more interested in "WHY DOES IT HAPPEN" part and if someone can explain to me in terms of Chemistry and Electrical Engineering involved I will be very glad.
Actually this recommendation is more for LiIon batteries - LiPo batteries don't seem so much affected by it. The reason I see most times is the self discharge in combination with the protection circuits. The protection circuitry disables the battery when it has been discharged too deep - recovering it from this state is non-ideal for the battery as well as requires a charger capable of trickle-charge preconditioning. To avoid this, the battery should be left in a state that is charged enough.
Also, a constant high charge level shortens the battery life. So its best to charge the battery to an intermediate level only.
Since LiPo batteries don't discharge as much, they are not so much affected by this problem.
In general, if a Lithium battery is stored fully charged at 25 degrees celcius for one year, it will lose approximately 20% of its capacity. Apparently if they are stored at a 40% state of charge, or at a much lower temperature, the loss of capacity is negligible. Thus the recommendation for the state of charge storage. I don't know if the liFe have the same problem. Sorry, I do not know why it happens.
