Do not overcharge cheap lithium battery devices.

[Geek-9pm]

This is NOT about cell phones. Instead, it is about those other things that your can charge from a USB port. Like a micro MP3 player.

You might buy a thing that has a rechargeable battery and plugs into your USB port.
Ignore people who tell you to charge it overnight. That is just wrong. I
8 hours might be for 4000 mah. The small batteries are 500 mah. The small, cheap light duty rechargeable batteries require only two hours to change on a USB port. And ignore those battery testers that tell you to recharge. Recharge only when the device stops performing. Be careful and expect the life to be a year or so.


Don't ask me for the research. Ask the people who tell you to leave it on the charterer. They are the ones who need to research charging norms for low-end lithium-ion  batteries used in cheep toys  and gs pocket devices.

[camerongray]

If a device's battery gets damaged by leaving it on charge overnight rather than for a couple of hours, I'd be concerned about the charge protection circuitry in the device.  Decent devices should have charge control chips that properly regulate charging and stop charging the battery when it is full.

[DaveLembke]

I'd say all rechargeable batteries should go through a cycle of charge and drain. Overcharging is dangerous and only the really cheap poorly constructed electronic chargers will maintain a constant charge even when the battery is at 100%.

I had a pile of smart phone crunching data for the BOINC Asteroids project for a while, but decided to shut them off from this data crunching because looking further into how the program ran on the smart phones, I didnt like that the program would only run when the battery was 100% charge and connected to a charger. Lithium batteries are dangerous if something goes wrong with them ( = usually a FIRE ), and are really meant to be cycled through a drain and charge cycle vs on a charger all the time.

So I have a bunch of spare smart phones that I picked up for $5 each if i need one, and they arent on the charge 24/7. 

[BC_Programmer]

IMO anything other than leaving a battery at 0% for a long time is pretty much fine. You can get compulsive about it but, at least in my experience, it doesn't make much of a difference.

Lithium Ion and Lithium Polymer batteries work best with Partial discharges, not full discharges. It is Nickel-Cadmium and Nickel-Metal Hydride batteries for which full discharge/charge cycles are best for their longevity. discharging a Li-Ion battery to 50%, charging it to full, then using it until it is at 50% again is considered a one cycle in terms of the rated number of cycles. For long term storage you want a partial/50% charge rather than empty or full. Empty could prevent it from being able to store much charge when one goes to use it again, and full can cause it to lose some capacity.

leaving it on the charger is similar to storage, so being fully charged will reduce it's lifespan.

Considering my Laptop from 2008 is coming up on 10 years old and sits on the charger pretty much 99% of the time and still runs for about an hour and a half (where, when new, it was 2 and a half hours) I'm not convinced it is worth the additional effort of worrying about specifically when, how, and at what percentages I should charge battery-based devices or the charge ratios I should remove them from the charger.

Even though the batteries are not typically consumer replaceable on many devices like MP3 Players, I've found the battery usually outlasts the device anyway. My 4GB Sony Walkman MP3 player from 2006 has basically fallen apart through normal usage. The case no longer stays together because the plastic for the screw posts snapped as did the little snaps in each side, so unless held together with tape or something the entire front comes off and the screen flaps in the breeze, it hangs frequently, the volume rocker fell off and a piece of metal had to be held across the snapped-off contacts where the microswitch used to be, and it's basically in a condition that makes it pretty much unusable as a portable MP3 Player, to the point that I replaced it for that reason. Despite this- the battery still powers the device for 6-7 hours (about half what it did when I bought it).

[Geek-9pm]

Corrections I said 500  mAh. I should have said 150 mAh as more typical of very small devices. Such batteries can be overcharged from a USB port. (Unless a over charge device is inserted in the circuit.)

If this is worrisome, don't by the cheap MP3 players from the far east. The battereies are not very well documented.

As I mentioned, this warning is about very small batteries found in low priced things like pocket MP3 players that do not have WiFi or LCD. Small batteries from 100 to 200 mAh are common.

Cheap devices are being sold both mail-order and in some stores. Be aware that the cheep models may have small batteries that can overcharge and present a possible fire hazards. Do not leave on the charger overnight.

This link below is about cells more typical for smart phones. Do not assume that the smaller batteries would meet some of these specs.
This is for compression.
https://www.ineltro.ch/media/downloads/SAAItem/45/45958/36e3e7f3-2049-4adb-a2a7-79c654d92915.pdf

Search for  data sheet 150 mAh battery

I found:
Far east maker:
https://cdn-shop.adafruit.com/datasheets/402025+150mAh.pdf
Above gives warnings about overcharge. Why?

Dmestic supplier:
https://media.digikey.com/pdf/Data%20Sheets/TinyCircuits%20PDFs/ASR00003_Web.pdf
Notice Digikey claims they sell units with built-in protection.

The above provides the technical specs. The battery itself  does not have  protection. It must be used in a device that prevents over charge, otherwise the user must monitor the charge to prevent damage.
Do not expect the low-cost MP3 players to have overcharge protection. One  MP3 player v vendor says do not ever charge for more than two hours. The data sheet for a typical 150 mAh battery above indicates a full charge can be done  in one hour.

EDIT: Here is a data sheet from Texas Instruments. This is not directly related to the topic, but gives a background about how battery chargers should work.
http://www.ti.com/lit/ds/symlink/bq2000t.pdf

[BC_Programmer]

When it comes to cheap chinese devices, you get what you pay for. I wouldn't be surprised if they lack certain protections or they don't function correctly. This is the same market where companies sell  you 2TB Flash drives for 40 bucks that are actually around 4GB.

Personally I think it is wiser not to buy cheap chinese crap that presents a risk of fire or explosion if I leave it plugged in for too long. But maybe I'm old-fashioned in my desire that my electronic devices not double as incendiary grenades.

[Salmon Trout]

I have a cheapo non-name Chinese mp3 player that I used for 5 years and then gave to my girlfriend who has used it now and then over another 3 years. It gets run to zero battery and left like that and then charged weeks later via USB ports, and in general, negelected according to the above. It is as good now as it was in 2009.

[DaveLembke]

I have a Prolynkz Zynxz 2GB MP3/MP4 player that I bought from Tiger Direct on the cheap around 2008 that I used lots and then lost it for a couple years and found it in a box of stuff when looking for a older 1GB DDR 266Mhz RAM stick that I remembered having and turning it on it was dead as in fully discharged, but found a cable to recharge it from my computers USB port and the music I put on its flash memory was still there and after a full charge it still worked and for hours of use as a MP3 player. I never used it for MP4 videos because the display is super small. I watched Hak5 episode on it once back before they were on youtube when they had their shows as downloads. Not sure if its Lithium or a niCad or NiMH battery in it. Never opened it up. But its still working after heavy use for a no name MP3/MP4 player and 9 years old on original rechargeable battery. I use it now at work on days that I have to go to work at 3am and this way I can work with music to stay awake and if it gets destroyed oh well I already got my moneys worth out of it. 

Ive used it for about 4 hours of MP3 and FM radio use at 70% volume in a noisy environment before the battery is spent from full charge and its impressive  that the battery hasnt wasted away for a cheap brand product. The microprocessor in it is weak its kind of laggy with the menu selection and you just need to press the button once and wait about 5 seconds as for if you press too fast it will be a navigation nightmare when it catches up with its instruction buffer from user and you overshot what you wanted and have to go back around again.

https://www.overstock.com/Electronics/Prolynkz-Zynxz-2GB-MP4-MP3-Player-with-FM-Radio/3233892/product.html