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Charging battery

:shock: we all know that xda2 stanby time accdg to O2 is 11hrs....HEllo!!
my unit lasts only for 6 hrs! Even if im lowering down my brightness
to the lowest. Can i charge my Li-ion bat even it still has 50%? will it
affect its life?...thnks

No, Li-Ion do not suffer from memory effect. That was the main problem with older Ni-Cads and to some extend in Ni-Mh.
On the contrary, never use up the whole charge of the Li-Ion battery, this will exhaust the battery and shorten its life.
Li-Ion can be charged when it has any amount of charge in it, But you must use the OEM charger, any other charger may harm the battery as it cant detect when the battery is full. Li-Ions are very sensitive for over charge and may be damaged.
But has in mind two things about Li-Ions, their life limit is about three years in the average and that Excess charging and discharging will use the cycle count (each time you connect your battery to a charger is called cycle, even if it is for a short moment) so don't use up your cycles limit which is about 500 in Li-Ion.
Also, be aware of heat, never make your battery suffer from heat and temps close to or above 60 C, each time you do that you lose about 20% of the capacity of your battery. (if you leave the battery in the direct sun for a while in some places in the world, this can easily make it's temp pass that limit, and the internal thermometer in the battery cant stop this damage, it is designed to stop charging the battery when it's temp rise while being charged).

Hatamata, that was very usefull information to share with us about the Lithium batteries..
Thanks a lot.

Nothing to thank me for my friend, I owe this site a lot

Batteries - fully discharge before recharging?

I always keep my pda in the cradle charging whenever I can (most of an average day) just like the instructions say so. A guy I work with says it's better for battery life to discharge them (near) fully and then recharge.
My battery life is now very short (after about 10 months use) and I am going to buy a replacement. Anyone know for sure which is the best way to keep batteries in good shape?
Thanks in advance ... Dr Firstpost

http://www.batteryuniversity.com/parttwo-34.htm
How to prolong lithium-based batteries
Battery research is focusing heavily on lithium chemistries, so much so that one could presume that all portable devices will be powered with lithium-ion batteries in the future. In many ways, lithium-ion is superior to nickel and lead-based chemistries and the applications for lithium-ion batteries are growing as a result.
Lithium-ion has not yet fully matured and is being improved continuously. New metal and chemical combinations are being tried every six months to increase energy density and prolong service life. The improvements in longevity after each change will not be known for a few years.
A lithium-ion battery provides 300-500 discharge/charge cycles. The battery prefers a partial rather than a full discharge. Frequent full discharges should be avoided when possible. Instead, charge the battery more often or use a larger battery. There is no concern of memory when applying unscheduled charges.
Although lithium-ion is memory-free in terms of performance deterioration, batteries with fuel gauges exhibit what engineers refer to as "digital memory". Here is the reason: Short discharges with subsequent recharges do not provide the periodic calibration needed to synchronize the fuel gauge with the battery's state-of-charge. A deliberate full discharge and recharge every 30 charges corrects this problem. Letting the battery run down to the cut-off point in the equipment will do this. If ignored, the fuel gauge will become increasingly less accurate. (Read more in 'Choosing the right battery for portable computing', Part Two.)
Aging of lithium-ion is an issue that is often ignored. Depending on the state-of-charge and storage temperature, lithium-based batteries have a typical lifetime of 2-3 years (longer if partially charged and kept cool). The clock starts ticking as soon as the battery comes off the manufacturing line. The capacity loss manifests itself in increased internal resistance caused by oxidation. Eventually, the cell resistance will reach a point where the pack can no longer deliver the stored energy, although the battery may still contain ample charge. Increasing internal resistance is common to cobalt-based lithium-ion, a chemistry that is found in laptops and cell phones. The lower energy dense manganese-based lithium-ion, also known as spinel, maintains the internal resistance through its life but loses capacity due to chemical decompositions.
The speed by which lithium-ion ages is governed by temperature and state-of-charge. Figure 1 illustrates the capacity loss as a function of these two parameters.
Figure 1: Permanent capacity loss of lithium-ion as a function of temperature and charge level.
High charge levels and elevated temperatures hasten permanent capacity loss. Improvements in chemistry have increased the storage performance of lithium-ion batteries.
There are no remedies to restore lithium-ion once worn out. A momentary improvement in performance is noticeable when heating up the battery. This lowers the internal resistance but the condition reverts back to its former state when the temperature drops.
If possible, store the battery in a cool place at about a 40% state-of-charge. Some reserve charge is needed to keep the battery and its protection circuit operational during prolonged storage. The most harmful combination is full charge at high temperature. This is the case when placing a cell phone or spare battery in a hot car. Running a laptop computer on the mains has a similar temperature problem. While the battery is kept fully charged, the inside temperature during operation rises to 45°C (113°F).
Removing the battery from the laptop when running on fixed power protects the battery from heat but some battery and laptop manufacturers caution against it. They say that dust and moisture accumulating inside the battery casing could damage the laptop. The dealers will be happy to provide you with a new pack when a replacement is needed a little sooner.
The question is often asked, should the laptop be disconnected from the main when not in use? With lithium-ion it does not matter. Once the battery is fully charged, no further charge is applied. It is recommended, however, to turn the laptop off overnight because heat harms the battery.
A large number of lithium-ion batteries for cell phones are being discarded under the warranty return policy. Some failed batteries are sent to service centers or the manufacturer, where they are refurbished. Studies show that 80%-90% of the returned batteries can be repaired and returned to service.
Some lithium-ion batteries fail due to excessive low discharge. If discharged below 2.5 volts per cell, the internal safety circuit opens and the battery appears dead. A charge with the original charger is no longer possible. Some battery analyzers (Cadex) feature a boost function that reactivates the protection circuit of a failed battery and enables a recharge. However, if the cell voltage has fallen below 1.5V/cell and has remained in that state for a few days, a recharge should be avoided because of safety concerns. To prevent failure, never store the battery fully discharged. Apply some charge before storage, and then charge fully before use.
All personal computers (and some other electronic devices) contain a battery for memory back up. This battery is commonly a small non-rechargeable lithium cell, which provides a small current when the device is turned off. The PC uses the battery to retain certain information when the power is off. These are the BIOS settings, current date and time, as well as resource assignment for Plug and Play systems. Storage does shorten the service life of the backup battery to a few years. Some say 1-2 years. By keeping the computer connected to the main, albeit turned off, a battery on the PC motherboards should be good for 5-7 years. A PC should give the advanced warning when battery gets low. A dead back-up battery will wipe out the volatile memory and erase certain settings. After battery is replaced, the PC should again be operational.
Simple Guidelines
Avoid frequent full discharges because this puts additional strain on the battery. Several partial discharges with frequent recharges are better for lithium-ion than one deep one. Recharging a partially charged lithium-ion does not cause harm because there is no memory. (In this respect, lithium-ion differs from nickel-based batteries.) Short battery life in a laptop is mainly cause by heat rather than charge / discharge patterns.
Batteries with fuel gauge (laptops) should be calibrated by applying a deliberate full discharge once every 30 charges. Running the pack down in the equipment does this. If ignored, the fuel gauge will become increasingly less accurate and in some cases cut off the device prematurely.
Keep the lithium-ion battery cool. Avoid a hot car. For prolonged storage, keep the battery at a 40% charge level.
Consider removing the battery from a laptop when running on fixed power. (Some laptop manufacturers are concerned about dust and moisture accumulating inside the battery casing.)
Avoid purchasing spare lithium-ion batteries for later use. Observe manufacturing date. Do not buy old stock, even if sold at clearance prices.
If you have a spare lithium-ion battery, use one to the fullest and keep the other cool by placing it in the refrigerator. Do not freeze the battery. For best results, store the battery at 40% state-of-charge.
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Created: February 2003, Last edited: June 2005
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About the Author
Isidor Buchmann is the founder and CEO of Cadex Electronics Inc
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V

The short answer.
No. Lithium batteries prefer to be topped up frequently and don't like being fully discharged.

Thanks TheBrit :wink:
Just to add - you can do damage to a lithium battery by entirely discharging it, so don't. Top up away. But expect to replace after a couple of years!
V

Thanks for the replys & detail.
Maybe my batteries are suffering from 'digital memory' - they have hardly ever been run down to device switch-off. For my new ones I'll try fully discharging every 30 recharges as suggested and see how that goes.
I'll post results of test in a years time!

I don't believe in topping them constantly. A friend and I bought our new phones 2 weeks apart from each other. I always heard to discharge them before charging, he on the other hand never cared. Just 6 months in now, his dies in 2 hours or less, with light use. I am playing music, surfing FB etc. all day long. Right now at 15 hours discharging and still 40% battery. He has charged his 5 times today due to phone going into low battery life, and only been up 11 hours.

It only happens with the Niquel-Cadmium not with the Lithium

jrodcamaro said:
I don't believe in topping them constantly. A friend and I bought our new phones 2 weeks apart from each other. I always heard to discharge them before charging, he on the other hand never cared. Just 6 months in now, his dies in 2 hours or less, with light use. I am playing music, surfing FB etc. all day long. Right now at 15 hours discharging and still 40% battery. He has charged his 5 times today due to phone going into low battery life, and only been up 11 hours.
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Wut

[INFO] Li-ion batteries myth busting

Updated and simplified version here : http://forum.xda-developers.com/showthread.php?p=3846897#post3846897
I've been around this forum for some time now and I have noticed one thing that is spelled in all sub-forums: BATTERY LIFE
So I thought of pulling some info together that is relevant to our Raphs (Li-ion batteries), taken from www.batteryuniversity.com.
Hope you find it helpful and understand better behaviour of your battery
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About the Author
Isidor Buchmann is the founder and CEO of Cadex Electronics Inc., in Vancouver BC.
Mr. Buchmann has a background in radio communications and has studied the behavior of rechargeable batteries in practical, everyday applications for two decades. Award winning author of many articles and books on batteries, Mr. Buchmann has delivered technical papers around the world.
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"If possible, do not discharge lithium-based batteries too deeply. Instead, recharge more often."
Lithium-ion is a low maintenance battery, an advantage that most other chemistries cannot claim. There is no memory and no scheduled cycling is required to prolong the battery's life. In addition, the self-discharge is less than half compared to nickel-cadmium, making lithium-ion well suited for modern fuel gauge applications.
Lithium-ion has not yet fully matured and is being improved continuously. New metal and chemical combinations are being tried every six months to increase energy density and prolong service life. The improvements in longevity after each change will not be known for a few years.
Charging
There is only one way to charge lithium-based batteries. The so-called 'miracle chargers', which claim to restore and prolong batteries, do not exist for lithium chemistries. Neither does super-fast charging apply. Manufacturers of lithium-ion cells have very strict guidelines in charge procedures and the pack should be charged as per the manufacturers "typical" charge technique.
Lithium-ion is a very clean system and does not need priming as nickel-based batteries do. The 1st charge is no different to the 5th or the 50th charge. Stickers instructing to charge the battery for 8 hours or more for the first time may be a leftover from the nickel battery days.
Most cells are charged to 4.20 volts with a tolerance of +/?0.05V/cell. Charging only to 4.10V reduced the capacity by 10% but provides a longer service life. Newer cell are capable of delivering a good cycle count with a charge to 4.20 volts per cell.
A lithium-ion battery provides 300-500 discharge/charge cycles. The battery prefers a partial rather than a full discharge. Frequent full discharges should be avoided when possible. Instead, charge the battery more often or use a larger battery. There is no concern of memory when applying unscheduled charges.
Batteries live longer if treated in a gentle manner. High charge voltages, excessive charge rate and extreme load conditions have a negative effect on battery life. The longevity is often a direct result of the environmental stresses applied. The following guidelines suggest ways to prolong battery life.
The time at which the battery stays at 4.20/cell should be as short as possible. Prolonged high voltage promotes corrosion, especially at elevated temperatures. Spinel is less sensitive to high voltage.
The lower charge current reduces the time in which the cell resides at 4.20V. A 0.5C charge only adds marginally to the charge time over 1C because the topping charge will be shorter. A high current charge tends to push the voltage into voltage limit prematurely.
Do not discharge lithium-ion too deeply. Instead, charge it frequently. Lithium-ion does not have memory problems like nickel-cadmium batteries. No deep discharges are needed for conditioning.
Do not charge lithium-ion at or below freezing temperature. Although accepting charge, an irreversible plating of metallic lithium will occur that compromises the safety of the pack.
Not only does a lithium-ion battery live longer with a slower charge rate; moderate discharge rates also helps.
Discharge of the lithium-ion battery is 5% in the first 24 hours after charge, and then reduces to 1% to 2% per month thereafter. The safety circuit adds about 3%. High cycle count and aging have little effect on the self-discharge of lithium-based batteries.
The battery industry is making incremental capacity gains of 8-10% per year. This trend is expected to continue. This, however, is a far cry from Moore's Law that specifies a doubling of transistors on a chip every 18 to 24 months. Translating this increase to a battery would mean a doubling of capacity every two years. Instead of two years, lithium-ion has doubled its energy capacity in 10 years.
Although lithium-ion is memory-free in terms of performance deterioration, batteries with fuel gauges exhibit what engineers refer to as "digital memory". Here is the reason: Short discharges with subsequent recharges do not provide the periodic calibration needed to synchronize the fuel gauge with the battery's state-of-charge. A deliberate full discharge and recharge every 30 charges corrects this problem. Letting the battery run down to the cut-off point in the equipment will do this. If ignored, the fuel gauge will become increasingly less accurate.
Despite its overall advantages, lithium-ion has its drawbacks. It is fragile and requires a protection circuit to maintain safe operation. Built into each pack, the protection circuit limits the peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. In addition, the cell temperature is monitored to prevent temperature extremes. The maximum charge and discharge current on most packs are is limited to between 1C and 2C. With these precautions in place, the possibility of metallic lithium plating occurring due to overcharge is virtually eliminated.
The worst condition is keeping a fully charged battery at elevated temperatures, which is the case with running laptop batteries. If used on main power, the battery inside a laptop will only last for 12-18 months. I must hasten to explain that the pack does not die suddenly but begins with reduced run-times.
The voltage level to which the cells are charged also plays an important role to longevity. For safety reasons, most lithium-ion cannot exceed 4.20 volts per cell. While a higher voltage boosts capacity, the disadvantage is lower cycle life.
"how deep can a battery be discharged and still achieve maximum service life?" There are no definite answers. Batteries are like us humans. Suppose we ate all the vegetables our mother heaped on our plates and do our daily exercise, would we life longer? Perhaps. But by how much, no one will know. Batteries lose capacity as part of aging, cycling and exposure to heat. Nickel-cadmium also loses capacity due to lack of exercise because of memory.
Some lithium-ion batteries fail due to excessive low discharge. If discharged below 2.5 volts per cell, the internal safety circuit opens and the battery appears dead.
Aging is a concern with most lithium-ion batteries and many manufacturers remain silent about this issue. Some capacity deterioration is noticeable after one year, whether the battery is in use or not.
Lithium-ion batteries lose capacity through cell oxidation, a process that occurs naturally during use and aging. The typical life span of lithium-ion is 2-3 years under normal use. Cool storage a 40% charge minimizes aging. An aged lithium-ion cannot be restored with cycling.
Shorted Cells
Cell reversal caused by deep discharging also contributes to shorted cells.Specified to deliver 100% capacity when new, the battery should be replaced when the capacity drops to below 80% of the nominal rating.
The self-discharge on all battery chemistries increase at higher temperatures. Typically, the rate doubles with every 10°C (18°F). A noticeable energy loss occurs if a battery is left in a hot vehicle.
Premature voltage cut-off
Not all stored battery power can be fully utilized. Some equipment cuts off before the designated end-of-discharge voltage is reached and precious battery energy remains unused. Applications demanding high current bursts push the battery voltage to an early cut-off. This is especially visible on batteries with elevated internal resistance. The voltage recovers when the load is removed and the battery appears normal. Discharging such a battery on a moderate load with a battery analyzer to the respective end-of-discharge threshold will sometimes produce residual capacity readings of 30% and higher.

Counterfeit cell phone batteries (clone batteries)
In the search for low-cost battery replacements, consumers may inadvertently purchase clone cell phone batteries that do not include an approved protection circuit. Lithium-ion packs require a protection circuit to shut off the power source if the charger malfunctions and keep on charging, or if the pack is put under undue stress (electrical short). Overheating and 'venting with flame' can be the result of such strain.
Cell phone manufacturers strongly advise customers to replace the battery with an approved brand. Failing to do so may void the warranty. Counterfeit cell phone batteries have become visible since the beginning of 2003 when the world was being flooded with cheap replacement batteries from Asia.
Cell phone manufacturers act out of genuine concern for safety rather than using scare tactics to persuade customers to buy their own accessories. They do not object to third party suppliers in offering batteries and chargers as long as the products are well built, safe and functioning. The buyer can often not distinguish between an original and a counterfeit battery because the label may appear bona fide.
Caution should also be exercised in purchasing counterfeit chargers. Some units do not terminate the battery correctly and rely on the battery's internal protection circuit to cut off the power when fully charged. Precise full-charge termination and a working protection circuit are needed for the safe use of the lithium-ion battery.
A large number of lithium-ion batteries for cell phones are being discarded under the warranty return policy. Some failed batteries are sent to service centers or the manufacturer, where they are refurbished. Studies show that 80%-90% of the returned batteries can be repaired and returned to service.
© Copyright 2003 - 2005 Isidor Buchmann

Great thread! Wiki!

Thanks
Tis is good info to know and to share. Thanks for putting this together for us all.

overcharging Fuze battery
When I exchanged my Fuze for a new one at AT&T, the service person said my battery was bad, due to overcharging. She said leaving my Fuze plugged into my car charger and my computer(with charging turned on) degraded the battery.
There is an option to NOT charge the battery when connected by USB to the computer.(kind of indicates no automatic charging control)
Well, I use my Fuze as a computer 12-14 hours a day. I want to see the screen, which means I need it plugged in either to the computer or car charger.
If I turn off recharging when connected to my computer, I end up with a dead battery pretty quickly, since I use it a lot as my business phone with a Bluetooth speakerphone.
The AT&T person said this information was given to them by HTC.

Thank you for the infos. Really need this cause battery life is my main concern.

recharge cycles
from reading other posts, it looks like the batteries have around 1000 recharge cycles.
Unfortunately, the cycles can occur every time you plug into your computer or charger, even if the charge goes from 99 to 100 %.
Which means I need a new battery probably every 9-12 months. Not too bad.

hrothnir said:
When I exchanged my Fuze for a new one at AT&T, the service person said my battery was bad, due to overcharging. She said leaving my Fuze plugged into my car charger and my computer(with charging turned on) degraded the battery.
There is an option to NOT charge the battery when connected by USB to the computer.(kind of indicates no automatic charging control)
Well, I use my Fuze as a computer 12-14 hours a day. I want to see the screen, which means I need it plugged in either to the computer or car charger.
If I turn off recharging when connected to my computer, I end up with a dead battery pretty quickly, since I use it a lot as my business phone with a Bluetooth speakerphone.
The AT&T person said this information was given to them by HTC.
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Which tells you how much you should listen to most AT&T people about technical issues and details. They were 100% wrong about the impact of charging continuously. And unless they were talking to an HTC hardware engineer...
It's more likely that your issues were simply caused by heavy use, which will cause any rechargeable battery to wear out more quickly. Most batteries I've seen will last between 500-1000 charging cycles, so if you're a heavy user and are wearing down your battery frequently, you'll "run through" those charging cycles more quickly.
The advice you were given is worth ignoring.

does it make any difference
Does it make any difference if i charge my fuze from a
- charger connected to power outlet
or
- an USB cable connected to compute
Obviously, the USB option takes longer time to charge completely.
I wanted to know, which is suggested?

hrothnir said:
from reading other posts, it looks like the batteries have around 1000 recharge cycles.
Unfortunately, the cycles can occur every time you plug into your computer or charger, even if the charge goes from 99 to 100 %.
Which means I need a new battery probably every 9-12 months. Not too bad.
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Charging from 99-100% definitely will not qualify as "One" cycle. Discharging from 100% to some 20% and then charging up may count as one cycle. Similarly, 5 or 6 shallow discharging and charging 60%-40%-60% can count as one cycle. It is much better for battery health though. charging momentarily for one or two minutes which increases the battery percentage by 2-3% will not count as a full cycle.

Discharging ("deep-cycling") your battery? STOP doing that.

If you like to deep-cycle (fully drain/recharge) their battery, you should stop doing that. Many of us got used to deep-cycling the Ni-Cd batteries, and didn't notice the smooth transition to Li-Ion batteries.
In fact, I can't think of a phone (or any other gadget) that would use Ni-Cd battery today. AFAIK, all modern phones/PDAs have Li-Ion batteries (including Raphael) which you SHOULD NOT fully discharge.
Here's a quote from wikipedia.org (http://en.wikipedia.org/wiki/Li-ion_battery):
Like many rechargeable batteries, lithium-ion batteries should be charged early and often. However, if they are not used for a long time, they should be brought to a charge level of around 40%–60%
Lithium-ion batteries should not be frequently discharged fully and recharged ("deep-cycled"), but this may be necessary after about every 30th recharge to recalibrate any electronic charge monitor (e.g. a battery meter). This allows the monitoring electronics to more accurately estimate battery charge.[27] This has nothing to do with the memory effect.
Li-ion batteries should never be depleted to below their minimum voltage, 2.4 V to 3.0 V per cell.
Li-ion batteries should be kept cool. Ideally they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. The high temperatures found in cars cause lithium-ion batteries to degrade rapidly.
Li-ion batteries should not be frozen [50] (most lithium-ion battery electrolytes freeze at approximately −40 °C; however, this is much colder than the lowest temperature reached by household freezers).
Li-ion batteries should be bought only when needed, because the aging process begins as soon as the battery is manufactured.[27]
When using a notebook computer running from fixed line power over extended periods, consider removing the battery[51] and storing it in a cool place so that it is not affected by the heat produced by the computer.
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Hope this helps someone.

Keeping the S3 plugged in all day. Problem?

Just ordered a dock for my S3 and was planning to use it at work, so the phone would be plugged into a charger 8hrs \ weekday. Will this kill my battery?

ubernewf said:
Just ordered a dock for my S3 and was planning to use it at work, so the phone would be plugged into a charger 8hrs \ weekday. Will this kill my battery?
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No. That doesn't affect LION batteries. have done it for years with tablets and other LION batteries.

ubernewf said:
Just ordered a dock for my S3 and was planning to use it at work, so the phone would be plugged into a charger 8hrs \ weekday. Will this kill my battery?
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No, lithium ion batteries have no battery memory like nickel cadmium ones. Charge whenever and as long as you want!

I let my phones, and my other Li-ion battery appliances charge everyday all night long. I can't imagine it being much different then charging while you're at work. Worst case scenario is your battery starts to not hold its charge a year from now, and then you could just get a new battery before the 1 year warranty is over.

I thought that while there is no memory effect with Li-ion batteries, they do die quickest when at maximum and minimum charge, and last longest when at 40-50% charge.
Per Wikipedia:
A Standard (Cobalt) Li-ion cell that is full most of the time at 25 °C (77 °F) irreversibly loses approximately 20% capacity per year. Poor ventilation may increase temperatures, further shortening battery life. Loss rates vary by temperature: 6% loss at 0 °C (32 °F), 20% at 25 °C (77 °F), and 35% at 40 °C (104 °F). When stored at 40%–60% charge level, the capacity loss is reduced to 2%, 4%, and 15%, respectively.[50] In contrast, the calendar life of LiFePO4 cells is not affected by being kept at a high state of charge.[51]
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Avoid deep discharge and instead charge more often between uses, the smaller the depth of discharge, the longer the battery will last.[106][unreliable source?]
Avoid storing the battery in full discharged state. As the battery will self-discharge over time, its voltage will gradually lower, and when it is depleted below the low-voltage threshold (2.4 to 2.9 V/cell, depending on chemistry) it cannot be charged anymore because the protection circuit (a type of electronic fuse) disables it.[106][unreliable source?]
Lithium-ion batteries should be kept cool; they may be stored in a refrigerator.[106][unreliable source?][107]
The rate of degradation of Lithium-ion batteries is strongly temperature-dependent; they degrade much faster if stored or used at higher temperatures.[106][unreliable source?][108]
The rate of degradation of Lithium-ion batteries is also related to battery charge level; they degrade much faster when at 100% charge, than at lower charges. Since batteries die if deep discharged (depleted) and since a battery has some self-discharge it is frequently recommended to store batteries at 40% charge level.[109]
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I'm not sure exactly which kind of Li-ion battery they are using as it seem some types are more immune to this effect than others.
But yeah, while it's not going to instantly kill your battery, it will cause it to lose capacity over time. This is the same reason why you shouldn't leave your laptop battery plugged in all the time.

I appreciate what you're doing there but I think it's hard to quote something as fact when it says "unreliable source" "unreliable source" "unreliable source" "unreliable source"...

Ha yeah I saw that but whatever. Wikipedia was just the first place I checked, I'm almost positive I've seen the same basic information elsewhere. And anecdotally I know I've laptop batteries stop holding charge after just a year or two when left plugged in 24/7.
This is also the reason that cell phones don't keep the battery charged at 100% when it's left plugged in. It goes to 100%, lets the battery die down to 90%ish, then charges back up to 100%, etc. It's trying to avoid keep the battery at 100%.