Questions conserve battery polymer lithium and lithium

[Audioguru]

Here is a video of a cheap "unknown chinese brand" battery:

 

[c_mitra]

If you have been using them already:

put them in the device and when the device battery status indicator says 50% charge is left, remove the battery and put in a plastic bag with some silica gel (dessicant). If they are brand new (freshly purchased), they are already 50% charged at the factory and you can store them in their original packing. After 1 year, exchange the stored battery with an used one (in the device).

 

[John rodrigues]

--- Updated Aug 29, 2020 ---

Even though it is a Chinese battery to keep at 50% of charge it will not go to zero charge after 1 year? this battery that I'm storing, I'm not going to put it in the device? I’m constantly using the device’s battery and when it dies I’ll use the battery that’s stored BP-5L and BM20 batteries

 

[Audioguru]

Did you try the cheap Chinese no-name-brand battery to see if it works? If it works then you should use it and store the good name-brand batteries.

 

[c_mitra]

Even though it is a Chinese battery to keep at 50% of charge it will not go to zero charge after 1 year?

If it does (gets fully discharged after 1 year) it was sick to start with. Most of the batteries are made in China and some are good and some are not. It depends the price you pay (you know the quality by the price you pay; unlike in the western countries where the quality and price are independent). The total capacity may reduce by 10% after 1 year (true for all makes)- 5000 mAH capacity battery shall lose about 500 mAH after 1-2 years.

--- Updated Aug 29, 2020 ---

The review appears rather credible. You may take a look if interested- a review of several 18650 li-ion cells.

 

[John rodrigues]

What is the main reason for storing the battery at 50% charge?

supposing that my BP-5L and BM20 battery has the lowest quality possible what is the discharge rate of it after 1 year stored?

 

[Audioguru]

www.batteryuniversity.com says that a fully charged or discharged Lithium battery in storage has a lot of chemical stress and fails soon. Maximum output power is reduced and the number of charge/discharge cycles are much less.

A battery that has the lowest quality possible does not work and is useless!
As shown on the videos, Name Brand high quality batteries work very well.

 

[c_mitra]

What is the main reason for storing the battery at 50% charge?

Is not trivial to explain. A battery has two electrodes: one positive terminal and one negative terminal. These two are separated by a, you guessed it, separator. That is all there in a battery.

The charge/ discharge graph for any arbitrary battery looks somewhat like this.

The x-axis (I have deliberately not labeled it) is the extent of charge /discharge. Because of the nature of the curve, the two extreme points are going to -infinity and +infinity. The y-axis is represented as the potential (just ignore the numbers; we are trying to see the general shape and features).

When a battery fails, it is most often the separator; the poor fellow is always under electrical and chemical stress. We need to minimize both.

The separator keeps the chemicals from the two side from mixing. They mix by diffusion and diffusion is more when there is a large concentration gradient.

The electric potential exerts a force on charge molecules and ions. However, this effect is most prominent very close to the electrode surface. It forms what is called an electric double layer.

When the charge state is 50% (middle of the graph above), the curve is almost horizontal. The reduced form and oxidised forms are equal. The diffusion pressure is also lowest.

You can see that there is nothing holy about 50%; you can make it 40% or 60% without any worries.

The above explanation is idealized and qualitative in nature. I have covered the important points, anyway.

 

[John rodrigues]

store the battery at 75% charge is good for conservation?

 

[c_mitra]

I do not have the datasheet for the batteries you are referring but I can see other Li-ion batteries. The behavior should be very similar (say within 10% or so apart from the overall capacity).

A real Li-ion battery has 3.7V at the terminals when 50% charged. About 10% charge, the voltage drops to around 3.5V and at 90% charge, the voltage will be around 3.9V. At 99% charged state, the voltage will be around 4.1V. At 1% charge left, the voltage will be 3.3V. You should not go outside these limits. A good battery will not self discharge below this voltage ever after 2-3 years (dry environment). For an ideal battery, these values will be 3.7V+/- 0.06V at 90%/10% point and 3.7V+/-0.12V at 99%/1% point. The reasons for this will shall not discuss.

For maximum life, cycle your battery only between 90%-10% levels. Do not leave for charging for long time (no trickle charging). If you store your battery at 75% charge (these values are approximated from the terminal voltage and are rough ideas), after 1 year you will certainly have 50% charge left.

But your mileage may vary. When I use new batteries in a device, after some time one of them dies before others. Li-ion batteries use fancy charging systems but I certainly do not know what goes on inside.

 

[Audioguru]

A normal lithium battery is 4.2V when fully charged. It is 3.2V when it cannot produce much power. It is 3.7V when half discharged.
But 3.2V is 76% of its total charging voltage.

 

[John rodrigues]

If I charge the battery up to 90 or 100% and store it, will it immediately be shortened by keeping it charged by 90 or 100% or will it take days or months?

 

[Audioguru]

If you store a high quality Lithium battery at a full charge then in a few months you will see that it has lost some power and has lost some capacity.
But if you store it at 3.7V to 3.8V per cell then it will be like new for many years.

Instead of asking the same question over and over, read about Lithium batteries at www.batteryuniversity.com .

 

[acelectric103]

To preserve the useful life of lithium batteries and lithium polymer it is necessary to keep them charged I have the removable batteries BP-5L and BM20, what is the monthly discharge rate of these batteries? would i have to carry them 1x per month?

Of course , you should charge them before you store.

 

[John rodrigues]

I have the BM20 battery and I charged it at 100% and I know a little bit now it is kept at 90-95%, if I store in this way the useful life of this battery will be reduced? is it the same to keep it at 50% or 95%?


i have this charger could i use it to discharge the battery for a very good charge to store? the charger shows 25, 50, 75, 100% on the display

 

[Audioguru]

Of course , you should charge them before you store.

You must charge or discharge to a storage charge which is 3.7V to 3.8V per cell, not a full charge.

--- Updated Sep 7, 2020 ---

Your charger does not say if it is made to charge one Lithium-ion battery cell.
It does not say if it can discharge a cell, and it probably cannot.

 

[John rodrigues]

So what should I do? I only have these two chargers and the BP-5L and BM20 batteries

 

[Audioguru]

When winter comes I store the Li-PO batteries for my model airplanes by discharging them into a car light bulb while I measure the voltage. When the voltage drops to 3.7V or 3.8V then they have the proper storage charge.

 

[John rodrigues]

I have nothing to measure the voltage, I only use these two chargers. Would you have any tips for properly charging these chargers and saving these batteries?

 

[Audioguru]

I am just guessing that when your charger shows a 50% charge then the battery voltage is at the storage voltage of 3.7V to 3.8V.