Questions batterys lithium

[tiago1986]

I am in doubt if these two BM20 and BP-5L batteries are lithium or lithium polymer batteries or lithium ions

the BP-5L batteries are 1800mah and the BM20 battery is 2000 I charged them using this photo charger for 75% after how many days do I need to recharge them again so they have long storage and durability?

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTXi58e_qNfzMCh8Kjr8ghv_fioU1COM08HvA&usqp=CAU
https://cf.shopee.com.br/file/247c2106d63885dc17be99b61824b8f1
https://www.dhresource.com/0x0/f2/albu/g8/M00/89/F0/rBVaVFzuMVGACHY8AAHs3FpwpDE386.jpg/universal-cellphone-battery-lcd-charger-single.jpg
https://www.dhresource.com/0x0/f2/albu/g4/M01/99/29/rBVaEFdqVmqAN_XSAAIMWAUWzYk355.jpg/mobile-universal-battery-charger-usb-port.jpg

[tiago1986]

Please help

[ejeffrey]

Those are lithium polymer cells.  The chemistry is basically the same but standard lithium ion are usually metal cylindrical cells while flat/rectangular cells are almost always lithium polymer.  Technically it doesn't have to be, you can make a polymer electrolyte cell rolled in a cylinder or a liquid electrolyte in a prismatic cell but it is very uncommon.

Regardless, self discharge depends on temperature, battery condition, and age, but takes about a year.  Topping them up every few months should be enough to keep them healthy.

[tiago1986]

I have xiaomi BM20 2000mah 4.2v and Chinese BP-5L 1800mah 3.7v batteries and I recharged it to 75% and stored it using this photo charger and I need to know how much I will recharge again to preserve battery life
temperature my home varies 31-34ºC

https://pt.aliexpress.com/item/32581647988.html

[ejeffrey]

It's not super sensitive, probably storing anywhere from 40-85% will avoid unnecessary damage.  Really if you that concerned about battery longevity you probably shouldn't be buying the cheapest batteries and chargers from aliexpress.

[tiago1986]

the BM20 battery is original xiaomi the seller said and it is more expensive, the Chinese BP-5L is a Nokia copy, the universal charger is the only one I know and it has a charge display

[NiHaoMike]

For long term storage, charge them to about 3.85V/cell and pack them with some desiccant in a ziploc type bag in the refrigerator. Allow them to warm up to room temperature before removing from bag for use.

[Siwastaja]

"Lithium polymer" is a marketing term. It doesn't have any technical meaning. It is sometimes, but not always, used to describe pouch cells. Pouch cells designated as either "li-ion" or "li-poly" have no difference.

There are other chemistry differences, though. Always refer to the correct datasheet of the exact product - if available, of course.

You do not need to maintenance charge li-ion cells. For best lifetime, keep at between 30-50%. Ignoring LiFePO4, in voltage, that would be roughly around 3.50 to 3.70V, depending on chemistry. 3.6V never goes wrong. At that state-of-charge, they won't practically self-discharge unless they are faulty. Maybe you can check the voltage every 2-3 years.

NiHaoMike's 3.85V is on the high side but really it doesn't matter that much, especially if he stores the cells in a refrigerator. Avoiding >3.9V and avoiding hot places is usually enough.

On the other hand, if they have a poorly designed permanently connected protection circuit pulling significant current, you may need to check the voltage periodically (like twice a year) and recharge if necessary.

[tiago1986]

is it true or myth that these BM20 2000mah 4.2v and BP-5L 3.7v 1800 batteries discharge slower with 30-50%??? i recharged them to 75% with this chinese charger

link charger
https://www.aliexpress.com/item/32880328764.html?spm=a2g0o.productlist.0.0.34b34c3aVrthkh&algo_pvid=8e6f96f2-6824-422e-8bc5-1c3aec313360&algo_expid=8e6f96f2-6824-422e-8bc5-1c3aec313360-21&btsid=0b0a556b16228892246966149e38c4&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

[Siwastaja]

It is true that self-discharge rate is higher at higher state-of-charge. Conversely, at lower state-of-charge there is less self-discharge. Temperature has similar effect: hotter = more self-discharge. I know this because I have measured this myself with various cells of LCO and NCA chemistries. Typical quality cells self-discharge approx. 1-6% of their capacity per year near full SoC at room temperature (+23 degC). At 50% SoC, the self-discharge is practically zero unless stored really hot.

At 75%, who knows? It's likely better than 100% but not necessarily nearly as good as 50%.

Self-discharge usually isn't of any concern at any SoC, any temperature. Irreversible damage, i.e., permanent loss of capacity or permanent loss of current handling capability, is. And this aging is similarly related to the state-of-charge and temperature as described above.

Nobody knows about your cells, though. They might be some random counterfeit crap which may or may not be of acceptable quality. It they self-discharge into oblivion, that doesn't matter; good cells do not self-discharge significantly. If they self-destruct, they were total crap to begin with.

Just use the cells for the intended purpose and replace with better ones if they die.

[tiago1986]

the temperature in my house varies between 31-34ºC what would be the best percentage of charge for self-discharge not to reduce the useful life of these batteries? BM20 and BP-5L batteries

Today I charge to 75% but I have to analyze my ambient temperature, percentage of charge and interval to perform a recharge before it goes down to %

[tunk]

As many have pointed out, there's a large variation on how cells behave.
The only way find out how your cells behave, is to check them periodically,
e.g. once a month. If you want to reduce self discharge, put them in a
sealed bag and then put them in the fridge.

[Siwastaja]

the temperature in my house varies between 31-34ºC what would be the best percentage of charge for self-discharge not to reduce the useful life of these batteries? BM20 and BP-5L batteries

Between 30% and 50% is best to reduce aging in such warm environment.

[tiago1986]

this temperature is the temperature of my region i can't change it and i don't have air conditioning so what's the best for my situation?

[Siwastaja]

Keeping between 30% and 50% is best in all situations for long-term storage. In yours, it's even more important. The answer is still the same: between approx. 30% and 50%. This isn't rocket science, 51% isn't magically bad. Even the 75% you are talking about is likely just fine.

[tiago1986]

I'm in doubt if I continue charging to 75% or 50% is better, my temperature is 31-34C high so 50% will drop faster for a dangerous charge its useful life? if I remember before I charge it to 50% but after 1 or 3 months I plugged the battery into the charger and it had dropped to 25%

[Siwastaja]

No, li-ion cells do not self-discharge into dangerously too low region by themselves. The self-discharge basically stops well before they are too empty. If a cell self-destructs in storage due to self-discharge, it was a bad cell to begin with.

You can safely charge or discharge a good cell to as low as 30% and put it on a shelf for 5 years if you want to.

Protection circuit may play games with you, though, and some broken-by-design protection circuits have caused destruction of cells. If a protection circuit is so badly broken it overdischarges a 30% cell into oblivion, using 50% storage instead doesn't give you much more margin, it will die anyway.

If unsure, measure voltage twice a year for example. It shouldn't go below about 3.45V.

If your cell has dropped from 50% to 25% during 1 to 3 months either your measurement shows wrong or the cell is faulty. Instead of the charger showing some percentage, I would trust a simple voltage measurement using a multimeter.

Faulty cells can behave any funny way and it isn't worth anyone's time to guess how they behave, just get some good cells.

[tiago1986]

I have the digital multimeter but I don't know how to test and which scale to use without damaging the battery? would you recommend recharging both to 50% and measuring with a multimeter? what is the best long-term storage voltage for these two batteries? BM20 4.2v 2000mah and BP-5L 3.7v 1800mah

[Siwastaja]

Let the cell rest for a few hours or a day before measuring. Be sure to measure using DC VOLTS mode in your multimeter, and make sure the test leads are plugged in the voltage measurement connectors. You can first measure a normal 1.5V or 9V alkaline battery to see you can do it right.

Be very careful not to accidentally short-circuit the pins while measuring.

Between 3.5V to 3.6V is the optimum long-term storage voltage for your cells, but up to 3.7V is still just fine.

[tiago1986]

does the test consist of DC volts on 200 scale? red and black tips connected to COM and 10A?

i want to test if the batteries have any damage caused by charging or storage and the other test is to find out if it is at the correct voltage for long term storage

for storage you said that up to 3.7v is enough but 3.7 is 100% battery and charge and not 50%

[tunk]

NO, this will short the cell.
Connect it to COM and V/ohm, and set it to the 20V DC range.

[tiago1986]

NO, this will short the cell.
Connect it to COM and V/ohm, and set it to the 20V DC range.

my multimeter

[Siwastaja]

Try to find a tutorial on how to measure a voltage with a multimeter. Definitely do NOT plug anything into the "10A" socket.

Try with a 9V battery first. It should read something between 8V and 10V if you do it correctly.

20V scale is more accurate than 200V scale when you want to measure a small voltage.

[tiago1986]

the correct is 20v scale and COM/VmA??

BM20 battery is 4.2v 100% and BP-5L is 3.7v 100%, for long term storage the V has to be half being 50%

[tunk]

They're both li-po cells with a fully charged voltage at 4.2-4.3V
and fully discharged at 3.0V. At half charge they're around 3.6V.
And do as Siwastaja suggests, find a tutorial.