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Question removable battery lithium

75% of charge is not good? i'm afraid to recharge by 50% and its self-discharge will be fast and in the future when i recharge it will be close to 0% i'm still confused about the months for a new recharge regardless of the battery brand
 

audioguru

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I just received some rechargeable Lithium AAA batteries and the manual that came with them said to recharge fully every three months, so I would do the same with yours.

20 year charge holding, don't think so, accepted wisdom is that Lithium batteries lose approx 5% charge per month, so in 20 months, they are flat.
Maybe the battery manual said to charge them every three months because they are cheap and with poor quality. Maybe they want you to charge them often and store them fully charged so that they "wear out" soon and you must buy new ones.

I use Li-PO rechargeable Lithium batteries in my RC model airplanes. The manufacturers say to store them over the winter at 3.7V to 3.8V which all of us do.
In October I discharge them to a storage voltage of 3.75V and 5 months later in March they are exactly the same voltage so I charge them and use them all summer. They last for years and are used hundreds of times each year. The airplanes vibrate the motor to warn me the battery is low at 3.2V then the motor is stopped at 3.0V but the receiver and servos still work for a controlled landing.

Maybe if I stored them fully charged at 4.2V then their voltage would drop 5% per month and be so "worn out" that they would need to be replaced.
My cell phone is almost always fully charged. Its battery is very worn out from being fully charged all the time that I must charge it every day. Its charge might not last one week when stored fully charged.
 

audioguru

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75% of charge is not good? i'm afraid to recharge by 50% and its self-discharge will be fast and in the future when i recharge it will be close to 0% i'm still confused about the months for a new recharge regardless of the battery brand
75% of what? 50% of what? 0% voltage will kill a lithium battery.
A lithium battery is 4.2V and has a low charging current when fully charged. About 3.6V is half charged. About 3.0V is zero charge and any lower then the battery is ruined.
 
I don't know anything about the quality of my battery I know I have a xiaomi BM20 and a Chinese BP-5L and the charger I posted charged them to 75% (the display shows 0%, 25%, 50%, 75%, 100%) but it's 75% 4.2V the BM20 battery
BP-5L battery is 75% of 3.7V

With this information I look for the answer if the 75% charge is good and how many months to recharge again without harming the life of the battery that has automatic discharge

help please
 

audioguru

Well-Known Member
Most Helpful Member
Many Chinese batteries are fakes or defective.
Your old charger (it has 2001 in it) might or might not charge properly and nobody knows what 755 is talking about.
75% of 3.7V is only 2.8V which is so low it damages a lithium battery.
You should lookup Lithium-Ion battery and see that it is 4.2V when fully charged, 3.7V is about half charged and its storage voltage. 3V is a very low voltage and less than 3V damages the battery.
 
If 75% of 3.7V is only 2.8V then are my batteries already permanently damaged?
can't I reverse this damage from this 3.7v battery? what percentage do i recharge to 3.7v?

the other BM20 battery is 4.2V charged at 75% what is the recommendation for it?
 

audioguru

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Most Helpful Member
A Lithium-ion battery with a voltage below about 3.0V is damaged and is dangerous because it might explode and/or catch on fire if charged from a simple old charger like you have. Read all about it at www.batteryuniversity.com .

Please do not say 75% anymore because nobody knows what it is.
 
So I'm going to throw the BP-5L 3.7V batteries in the trash? permanently damaged ?

should i have charged at 3.7v for what percentage?
 

audioguru

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Please read about the details of batteries. In my country, worn out or low voltage batteries are recycled.
A Lithium-Ion battery is not charged at 3.7V, instead it is sold at the storage voltage of 3.7V. A full charge is 4.2V plus a low changing current.
 
If storing the 3.7v battery with a 75% charge is bad for its useful life then you should never store these batteries at a 50% charge? some people say store is not 100% but at 50%

What is the email from battery university? I contacted them but they don't respond
 

audioguru

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Why don't you understand that a 75% charge or 50% charge does not say what the percentage is for? Voltage? Current? Is it for mAh?
A Lithium Ion battery is 4.2V when fully charged and the charging current has dropped to a low amount.
A voltage of 3.2V produces a very low power output.
Then the voltage is about 3.7V when the battery is half charged and is the storage and selling voltage.
If you store a Lithium-Ion battery at a 4.2V full charge then its lifetime, power output and capacity are shortened.

You do not contact battery university, instead you read what their experts say about batteries.
 

rjenkinsgb

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Just put them in something that has a multi-level or percentage indicator for charge level. Run them flat then charge to somewhere around half charge according to the device charge indicator.

They will be fine.

Battery University explicitly says do NOT try to calculate state of charge from voltage as the mid charge voltage "slope" is too flat.

Article here; "AirShip" section covers setting a percentage charge state:
 

Nigel Goodwin

Super Moderator
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I need to contact them because my questions are specific

what is your recommendation for my batteries?
Stop paying attention to your crap Chinese charger - the imaginary 75% indication is totally meaningless, and almost certainly doesn't mean what you (and AudioGuru) seem to think. You don't measure Li-Ion battery charge (or any other) from zero volts upwards.

'Possibly' 0% will be around 3V, and 100% 4.2V - but the cheap charger doesn't tell you what it means.
 
Stop paying attention to your crap Chinese charger - the imaginary 75% indication is totally meaningless, and almost certainly doesn't mean what you (and AudioGuru) seem to think. You don't measure Li-Ion battery charge (or any other) from zero volts upwards.

'Possibly' 0% will be around 3V, and 100% 4.2V - but the cheap charger doesn't tell you what it means.
I do not have another charger and its advantage is that it is universal. What is your recommendation for charging using this charger for these BM20 2000mah 4.2v and BP-5L 1800mah 3.7v batteries? what is the frequency of charging these batteries for long life and storage? i put 75% is good or bad?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I do not have another charger and its advantage is that it is universal. What is your recommendation for charging using this charger for these BM20 2000mah 4.2v and BP-5L 1800mah 3.7v batteries? what is the frequency of charging these batteries for long life and storage? i put 75% is good or bad?
As I've already said, we've no idea what this '75%' actually is - it's just an arbitrary figure from the Chinese manufacturer.

If it's any 'help' here's a charging curve, showing current and voltage, from one of my 4S battery packs.

Charging curve.png
 
Using a digital multimeter is it possible to test the charger is 75%?

this charger especifications
Input: AC 110-240 V 50/60Hz
Output: DC 4.2 V DC 400 mA max
 
Last edited:

audioguru

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Most Helpful Member
Maybe the cheap charger shows its guess of "percentage of charging time"?
We do not know if the cheap charger wrongly shuts off when the voltage reaches 4.2V when the graph posted by Nigel shows that then the battery is far from a full charge.

The battery university has a graph of discharge voltage that I disagree with. I found another discharge graph that looks correct:
 

Attachments

75% believe to be 4.2v or 3.7v the charger shows on the lcd 25% or 50 or 75 or 100% so I look for a good charge to store these batteries and they have long life
 

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