iPhone 4, iPhoe 3G and iPhone 3GS have a very good and long time battery life because a thinner and lighter LiPo battery was built in them. But we can also get some simple tips to improve your iPhone battery life for a longer time.
Turn on iPhone WiFi You can get a WiFi network when you are at home, work or other places. So it’s easy to get a better battery life when you shift your iPhone from 3G to WiFi. If you don’t know it, just change setting apps and slide WIFI to “on”, then log on the networks.
When you don’t want using WiFi network to surfing at home or work. Stop WiFi app will save lots of iPhone battery life. Because WiFi radio is scanning all the time and kill the LiPo battery in your iPhone.
Bluetooth app in your iPhone is also keep scanning the other Bluetooth when you turn on it for transferring files but forget turning off it. It’s easy to change it in setting apps. Turn it on when you want to receive some files from the other iPhone of your friends. It’s a good way to improve your iPhone battery life.
Push notifications are friendly to ask you allow or not when you install new apps such as QQ, goolgemaps or other apps in your iPhone 4. But most of time you clearly know what you are installing, so push notifications is redundant and harm your iPhone battery life.
Turn down iPhone Screen Brightness
Phone 4 and other touch screen phone have a big screen for easy operating and good view. But the LiPo battery have a problem, it need a longer and longer battery life to hold on. I believe you don’t want a big phone looks like a brick. So turn down screen brightness, we can get a longer battery life.
When you know clearly where you want to drive, you have to turn off Streaming and Navigation apps, We will not stop extending our iPhone battery life.
Maybe your 3G service is going on when you bought your iPhone 4 and 3G radio is scanning possible 3G network service even in your pocket. Now you have to use auto 3G. It’s a so good apps to turn off your iPhone 3G radio off when the screen locked. When you take on your iPhone, it will auto connect 3G networks.
Even LiPo battery have no memory, but when you overdo your iPhone battery, it will also kill your battery life. The best time to charge iPhone is when you see low power notification. You can charge your iPhone battery when you sleep in the night even it’s 50% or 30% of power then you can have good power in day.
After analysis the loss capacity of LiPo battery, we got the main reason is overcharge that charging voltage is over the prescriptive voltage (4.2V) and then keep charging. In this process of overcharge will result in loss capacity of LiPo battery. The main points are as follow
▪The overcharge of graphite anode of LiPo battery
▪The overcharge of positive reaction of LiPo battery
▪The oxidizing of electrolyte when overcharging
Lithium ion will be easy deposited on the cathode and stop lithium ion implanted. The efficiency of discharge and capacity of LiPo battery will be lost.
▪The circulatory lithium ion will be reduced.
▪The deposit lithium ion of metal will be reacted with electrolyte to Li2CO3 and LiF.
▪The lithium ion of metal will be happened between negative and septum, and it may increase internal resistance of LiPo battery.
Rapid charging is anther way to loss capacity of LiPo battery. When we doing rapid charging LiPo battery, discharge current is high, polarization will be happened on cathode, lithium ion will deposit obviously. The main reason of loss capacity of LiPo battery when we rapid charging is the matter of electronic chemical inertness, such as Co3O4, Mn2O3 and so on. They break the balance of capacity between cathode and anode. But the losing capacity of LiPo battery is irreversible.
Self discharge of LiPo battery is the losing capacity when the battery is not using. It have two condition when self discharge happened. No.1 is reversible losing capacity and No.2 is irreversible losing capacity. Reversible losing capacity is the capacity of LiPo battery will be recovered in next charging. Irreversible losing capacity is that the capacity of LiPo battery can’t be recovered in next charging. The influencing factor have the material of cathode/anode, technology, temperature and so on.
Lithium ion polymer battery, polymer lithium ion, or more commonly lithium polymer batteries (Li-poly, Li-Pol, LiPo, LIP, PLI or LiP) are rechargeable batteries. Normally batteries are composed of several identical secondary cells in parallel addition to increase the discharge current capability.
A research team at Japan's Advanced Industrial Science and Technology has developed a new anode technology that could boost the lifespan of a lithium ion polymer batteries charge by as much as 30 percent. The synthesis method, known as "soft chemistry," creates a titanium oxide that is significantly more efficient than the lithium ion titanate it would replace. LiPo battery could generate about 225mAh of power for each gram versus 175mAh today.
The technique can run at a relatively low temperature, making it easier to implement, and could also reduce the cost of the batteries themselves. Titanium oxide doesn't require relatively costly lithium to make, AIST said. Switching also doesn't affect the ability to maintain capacity over repeated charges. Researchers didn't say how soon they expected the new developments to find their ways into shipping products, though the development is relatively conventional and might become practical sooner than usual for battery research.
Cells sold today as polymer batteries are pouch cells. Unlike lithium-ion cylindrical cells, which have a rigid metal case, pouch cells have a flexible, foil-type (polymer laminate) case. In cylindrical cells, the rigid case presses the electrodes and the separator onto each other; whereas in polymer cells this external pressure is not required because the electrode sheets and the separator sheets are laminated onto each other.
Since individual pouch cells have no strong metal casing, by themselves they are over 20% lighter than equivalent cylindrical cells. However, all Li-Ion cells expand at high levels of SOC; if uncontained, this may result in delamination, and reduction of reliability and cycle life; the case of cylindrical cells provides that containment, while pouch cells, by themselves, are not contained. Therefore, to achieve the rated performance, a battery composed of pouch cells must include an overall, strong, external casing to retain its shape.
The voltage of a Li-poly cell varies from about 2.7 V (discharged) to about 4.23 V (fully charged), and Li-poly cells have to be protected from overcharge by limiting the applied voltage to no more than 4.235 V per cell used in a series combination. Overcharging a Li-poly battery can cause an explosion or fire. During discharge on load, the load has to be removed as soon as the voltage drops below approximately 3.0 V per cell (used in a series combination), or else the battery will subsequently no longer accept a full charge and may experience problems holding voltage under load. This can be achieved, as with other lithium-ion batteries, also harmed by under- and over-voltage, by circuitry that prevents overcharge and deep discharge.
Early in its development, lithium polymer technology had problems with internal resistance. Other challenges include longer charge times and slower maximum discharge rates compared to more mature technologies. Li-poly batteries typically require more than an hour for a full charge. Recent design improvements have increased maximum discharge currents from two times to 15 or even 30 times the cell capacity (discharge rate in amperes, cell capacity in ampere-hours). In December 2007 Toshiba announced a new design offering a much faster rate of charge (about 5 minutes to reach 90%). These cells were released onto the market in March 2008 and are expected to have a dramatic effect on the power tool and electric vehicle industries, and a major effect on consumer electronics.
When compared to the lithium-ion battery, Li-poly has a greater life cycle degradation rate. However, in recent years, manufacturers have been declaring upwards of 500 charge-discharge cycles before the capacity drops to 80% (see Sanyo). Another variant of Li-poly cells, the "thin film rechargeable lithium battery", has been shown to provide more than 10,000 cycles.
A compelling advantage of Li-poly cells is that manufacturers can shape the battery almost however they please, which can be important to mobile phone manufacturers constantly working on smaller, thinner, and lighter phones.
Li-poly batteries are also gaining favor in the world of radio-controlled aircraft as well as radio-controlled cars, where the advantages of both lower weight and greatly increased run times can be sufficient justification for the price. Some airsoft gun owners have switched to LiPo batteries due to the above reasons and the increased rate of fire they provide. However, lithium polymer-specific chargers are required to avoid fire and explosion. Explosions can also occur if the battery is short-circuited, as tremendous current passes through the cell in an instant. Radio-control enthusiasts take special precautions to ensure their battery leads are properly connected and insulated. Furthermore fires can occur if the cell or pack is punctured. Radio-controlled car batteries are often protected by durable plastic cases to prevent puncture. Specially designed electronic motor speed controls are used to prevent excessive discharge and subsequent battery damage. This is achieved using a low voltage cutoff (LVC) setting that is adjusted to maintain cell voltage greater than (typically) 3 V per cell.
Li-poly batteries are also gaining ground in PDAs and laptop computers, such as Apple's MacBook family, Amazon's Kindle, Lenovo's ThinkPad X300 and Ultrabay Batteries, the OQO series of palmtops, the HP Mini and Dell products featuring D-bay batteries. They can be found in small digital music devices such as iPods, Zunes, and other MP3 players and the Apple iPhone and iPad, as well as gaming equipment like Sony's PlayStation 3 wireless controllers. They are desirable in applications where small form factors and energy density outweigh cost considerations.
These batteries may also power the next generation of battery electric vehicles. The cost of an electric car of this type is prohibitive, but proponents argue that with increased production, the cost of Li-poly batteries will go down. Hyundai Motor Company plans to use this battery type in its hybrid electric vehicles. A Li-poly powered Audi A2 covered the record distance of 600 km without recharging on October 26, 2010.
There are currently two commercialized technologies, both lithium-ion-polymer (where "polymer" stands for "polymer electrolyte/separator") cells.
These are collectively referred to as "polymer electrolyte batteries". The battery is constructed as: Cathode: LiCoO2 or LiMn2O4 Separator: Conducting polymer electrolyte Anode: Li or carbon-Li intercalation compound Typical reaction: Anode: carbon–Lix → C + xLi+ + xe− Separator: Li+ conduction Cathode: Li1−xCoO2 + xLi+ + xe− → LiCoO2 Polymer electrolytes/separators can be solid polymers (e.g., polyethyleneoxide, PEO) plus LiPF6, or other conducting salts plus SiO2, or other fillers for better mechanical properties (such systems are not available commercially yet). Some manufacturers like Avestor (since merged with Batscap) are using metallic Li as the anode (these are the lithium-metal-polymer batteries), whereas others wish to go with the proven safe carbon intercalation anode. Both currently commercialized technologies use PVdF (a polymer) gelled with conventional solvents and salts, like EC/DMC/DEC. The difference between the two technologies is that one (Bellcore/Telcordia technology) uses LiMn2O4 as the cathode, and the other the more conventional LiCoO2. Other, more exotic (although not yet commercially available) Li-polymer batteries use a polymer cathode. For example, Moltech is developing a battery with a plastic conducting carbon-sulfur cathode.
However, as of 2005 this technology seems to have had problems with self-discharge and manufacturing cost. Yet another proposal is to use organic sulfur-containing compounds for the cathode in combination with an electrically conductive polymer such as polyaniline. This approach promises high power capability (i.e., low internal resistance) and high discharge capacity, but has problems with cycleability and cost.
Analog front ends that balance cells and eliminate mismatches of cells in series or parallel significantly improve battery efficiency and increase the overall pack capacity. As the number of cells and load currents increase, the potential for mismatch also increases. There are two kinds of mismatch in the pack: state-of-charge (SOC) and capacity/energy (C/E) mismatch. Though the SOC mismatch is more common, each problem limits the pack capacity (mA·h) to the capacity of the weakest cell. Battery pack cells are balanced when all the cells in the battery pack meet two conditions: If all cells have the same capacity, then they are balanced when they have the same relative state of charge (SOC). In this case, the open circuit voltage (OCV) is a good measure of the SOC. If, in an out-of-balance pack, all cells can be differentially charged to full capacity (balanced), then they will subsequently cycle normally without any additional adjustments. If the cells have different capacities, they are also considered balanced when the SOC is the same. But, since SOC is a relative measure, the absolute amount of capacity for each cell is different. To keep the cells with different capacities at the same SOC, cell balancing must provide differential amounts of current to cells in the series string during both charge and discharge on every cycle.
LiPoly batteries must be charged carefully. The basic process is to charge at constant current until each cell reaches 4.2 V; the charger must then gradually reduce the charge current while holding the cell voltage at 4.2 V until the charge current has dropped to a small percentage of the initial charge rate, at which point the battery is considered 100% charged. Some manufacturers specify 2%, others 3%, but other values are also possible. The difference in achieved capacity is minute. Balance charging simply means that the charger monitors the voltage of each cell in a pack and varies the charge on a per-cell basis so that all cells are brought to the same voltage. It is important to note that trickle charging is not acceptable for lithium batteries; Li-ion chemistry cannot accept an overcharge without causing damage to the cell, possibly plating out lithium metal and becoming hazardous. Most manufacturers claim a maximum and minimum voltage of 4.23 and 3.0 volts per cell. Taking any cell outside these limits can reduce the cell's capacity and ability to deliver full rated current. Most dedicated lithium polymer chargers use a charge timer for safety; this cuts the charge after a predefined time (typically 90 minutes).
Unlike certain other types of batteries, lithium polymer batteries can be stored for one or two months without significantly losing charge. However, if storing for long periods, manufacturers recommend discharging the battery to 40% of full charge. In addition, other sources recommend refrigerating (but not freezing) the cell.
With a little bit of care, you can maximize the battery life (i.e. the time your battery will run before it must be recharged) and lifespan of your notebook's battery. Most importantly, use your Apple notebook in its comfort zone for temperature (See “Notebook Temperate Zone”). Don’t leave it locked in a hot trunk during the summer.
Your New Notebook
Your new Apple notebook features advanced battery chemistry that greatly extends the battery’s lifespan. The built-in battery of your MacBook, MacBook Pro or MacBook Air is designed to deliver up to 1000 full charge and discharge cycles before it reaches 80 percent of its original capacity. In addition, Adaptive Charging reduces the wear and tear on the battery giving it a lifespan of up to 5 years. Be sure to fully charge your portable when you plug it in for the first time, and then run Software Update to ensure you have the latest software. Apple periodically releases updates that may improve battery performance.
For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Apple does not recommend leaving your portable plugged in all the time. An ideal use would be a commuter who uses her notebook on the train, then plugs it in at the office to charge. This keeps the battery juices flowing. If on the other hand, you use a desktop computer at work, and save a notebook for infrequent travel, Apple recommends charging and discharging its battery at least once per month. Need a reminder? Add an event to your desktop’s iCal. When your battery no longer holds sufficient charge to meet your needs, you may choose to replace it. If your notebook came with a built-in battery, you should have the battery replaced only by an Apple Authorized Service Provider.
If you don’t plan on using your notebook for more than six months, Apple recommends that you store the battery with a 50% charge. If you store a battery when it’s fully discharged, it could fall into a deep discharge state, which renders it incapable of holding any charge. Conversely, if you store it fully charged for an extended period of time, the battery may experience some loss of battery capacity, meaning it will have a shorter life. Be sure to store your notebook and battery at the proper temperature. (See “Notebook Temperate Zone.”)
You can choose to use your Apple notebook in a way that maximizes its battery life.
Energy: The Energy Saver control panel offers several settings that determine power levels for your PowerBook. Your portable knows when it’s plugged in, and runs accordingly. When on battery power, it will dim the screen and use other components sparingly. If you change this setting to maximize performance, your battery will drain more quickly.
Brightness: Dim the screen to the lowest comfortable level to achieve maximum battery life. For instance, when watching a DVD on an airplane, you may not need full brightness if all the lights are off.
AirPort Wireless: AirPort consumes power, even if you are not using its features to connect to a network. You can turn it off in its control panel to save power.
Bluetooth Wireless: Likewise, you can turn off Bluetooth to maximize your battery life, as it also consumes power when not in use.
Applications and peripherals: Disconnect peripherals and quit applications not in use. Eject CDs and DVDs if not currently accessing them.
Lithium polymer batteries are volatile. Failure to read and follow these instructions may result in fire, personal injury and damage to property if charged or used improperly.
LiPol Battery, its distributors and retailers assume no liability for failures to comply with these warnings and safety guidelines.
By purchasing this battery, the buyer assumes all risks associated with this product. If you do not agree with these conditions, please return the battery immediately before use.
General Guidelines and Warnings
1) LiPol Battery batteries are NOT charged as you receive them. They contain approximately 50% of a full charge.
2) Use Lithium Polymer specific chargers only. Do not use a NiCd or NiMh charger -Failure to do so may cause a fire, which
may result in personal injury and property damage.
3) Never charge batteries unattended. When charging LiPo batteries you should always remain in constant observation to monitor the charging process and react to potential problems that may occur.
4) Some LiPo chargers on the market may have technical l deficiencies that may cause them to charge LiPo batteries incorrectly. It is solely the responsibility of the user to assure that the charger used works properly. LiPol Battery only recommends chargers and balancers made by LiPol Battery, other brands may work but are out of LiPol Battery’s control.
5) If at any time you witness a battery starting to balloon or swell up, discontinue the charging process immediately. Disconnect the battery and place it in a safe observation area for approximately 15 minutes. Continuing to charge a battery that has begun to swell will result in fire.
6) Battery observation should occur in a safe area outside of any building or vehicle and away from any combustible material. The middle of a cement driveway is a good example of a safe observation area .
7) Shorts can cause fires! If you accidentally short the wires, the battery must be placed in a safe area for observation for approximately 15 minutes. Additionally, be mindful of the burn danger that may occur due to a short across jewelry (such as rings on your fingers).
8) Chemical reactions are not instantaneous, a battery that has been shorted may not ignite for 10 minutes. 9) All crash batteries, even if not deformed, should be placed in a safe area for observation for at least 15 minutes 10) If for any reason you need to cut the terminal wires, cut each wire separately, ensuring the wires do not become shorted across
the cutting tool.
11) When soldering connectors, first place a short length of heat shrink tubing over each wire. Then remove the insulating tape from the red wire and strip a short length of the insulation off, exposing the conductor approximately ¼”. Tin the exposed wire as well as the connector terminals. Place the wire in contact with the positive connector terminal and re -flow the solder of both together. Once cool, slide the heat shrink tubing down to cover the joint and shrink. Repeat the process for the black wire. If you accidentally short the battery wires, place the battery in a safe area and observe it for approximately 15 minutes.
12) Never store or charge a battery pack inside your car if the internal temperature will exceed 120 degrees
Before the First Charge for LiPo battery
1) Make a visual inspection of the pack. Checking for any damaged leads, connectors, broken/cracked shrink covering, puffiness or other irregularities.
2) Before installing or changing the connector, check the voltage of the pack using a digital voltmeter (not your charger). All new packs ship at approximately 3.80V to 3.9V per cell. For example: A 2S pack should read approximately 7.60V to 7.8V, A 3S pack should read approximately 11.40V to 11.7V.
3) If any damage to the pack or leads is found, or the voltage is significantly less for your pack than specified above, do not attempt to charge or fly the pack; contact LiPol Battery directly as soon as possible. Charging Process 1) Never charge batteries unattended.
2) Charge in an isolated area, away from flammable materials.
3) Let the battery cool down to ambient temperature before charging.
4) Do not charge battery packs in series except as outlined in step 8. Charge each battery pack individually. Overcharging of one or the other battery may occur resulting in fire. ***In order to discharge packs in series, the charged voltage of each cell in both packs must be within 0.01V***
5) When selecting the cell count or voltage for charging purposes, select the cell count and voltage as it appears on the battery label. Selecting a cell count or voltage other than the one printed on the lab el may result in overcharging and fire. As a safety precaution, please confirm that the information printed on the battery is correct. For example: If a battery label indicates that it is a 3 cell battery (3S), its voltage should read between 11.4 and 11.7 volts. This battery must be charged as a 3 cell battery (peak of 12.6V).
6) You must check the pack voltage after each flight before re-charging. Do not attempt to charge any pack if the unloaded individual cell voltages are less than 3.3V. For example: Do not charge a 2-cell packs if below 6.6V
Do not charge a 3 cell pack if below 9.9V
7) NORMAL CHARGING: The charge rate should not exceed 1C (one times the capacity of the battery, unless otherwise noted*). Higher setting may cause problems which can result in fire. For example: Charge a 730mAh battery at or below 0.73Amps. Charge a 5000mAh battery at or below 5Amps.
LiPol Battery packs with balancing connectors can be used with TP balancers for safer charging. For
more information, please visit: www.thunderpowerrc.com
*To charge at greater than 1C (no more than 3C): You must use a LiPol Battery 1010C charger in
conjunction with a LiPol Battery Balancer (205 or 210) and data cable. Only Polite 910, 1320, 2000 and
2100 cells qualify for charging up to 3C.
8) To charge two packs in series: The packs need to first be charged individually (using a 1010C, 210V balancer and associated data cable), and flown in series for a couple of cycles. Then, having flown both packs together in series, using a good quality DVM, check the individual cell voltages at the balancing connector. If all the voltages are within 0.01V of each other, series charging should be safe. Please note that this requires a “Y” cable be made to electrically attach the packs together in series and that the battery on the negative most side of this cable (the lead that goes to the negative terminal of the charger) be attached to “group A” of the balancer. Please see 1010C/210V instructions.
First few Flights
LiPol Battery recommends no more than 3-5C average discharge for breaking in new packs. Also be extremely careful not to over discharge new packs (Packs should NEVER be over discharged at any time, but over discharging on the first flight will ruin the battery
permanently before you are able to enjoy it. See “Caring for Battery” below).
Storage & Transportation 1) Store batteries at room temperature between 40 and 7 0 degrees F for best results. 2) If storing longer than one week; batteries must be stored at 3.8V/cell to 3.9V/cell (approximately 50% charged). This is easily accomplished using the LiPol Battery 1010C charger. 3) Do not expose battery packs to direct sunlight (heat) for extended periods. 4) When transporting or temporarily storing in a vehicle, temperature range s should be greater than 20 degrees F but no more than 150 degrees F. 5) Storing Lipo batteries at temperatures greater than 170 degrees F for extended periods of time (more than 2 hours) may cause damage to battery and possible fire.
Caring for Battery 1) Only charge a LiPo battery with a good quality Lithium Polymer charger. A poor quality charger can be dangerous. All LiPol Battery chargers & Balancers are of the highest quality available. 2) Set voltage and current correctly (failure to do so can cause fire). 3) Please check pack voltage after the first charge. For example; a 2 Cell battery should measure 8.4V (8.30 to 8.44), a 3 cell battery should measure 12.6V (12.45 to 12.66). 4) Do not discharge a battery to a level below 3V per cell under load. Discharging below 3V per cell can deteriorate battery performance. Be sure to set your ESC for the proper cut off voltage (6.0V cut off for 2S packs, 9.0V cut off for 3S packs, etc). 5) Use caution to avoid puncture of the battery. Puncturing a LiPo battery may cause a fire.
Charge: 32 to 113 degrees F
Discharge: 32 to 140 degrees F
1) Always allow a battery to cool down to ambient temperature before re-charging.
2) During discharge and handling of batteries, do not exceed 160 degrees F.
Battery Life Batteries that lose 20% of their capacity must be removed from service and disposed of properly.
Discharge the battery to 3V/Cell, making sure output wires are insulated, then wrap battery in a bag for disposal.
Product warranty is limited to original defects in material and workmanship for 90 days from the day of purchase. Warranty does
not cover collateral damage, misuse, abuse, incorrect charging and other inappropriate use of this product.
Today’s LiPo battery research is heavily focused on lithium ion chemistries, so much so that one could assume that all future batteries will be lithium systems. Lithium ion polymer batteries offer many advantages over nickel and lead-based systems. Although maintenance free, no external service is known that can restore the battery’s performance once degraded.In many respects, Lithium ion provides a superior service to other chemistries, but its performance is limited to a defined lifespan.
The Lithium ion battery has a time clock that starts ticking as soon as the battery leaves the factory. The electrolyte slowly eats up the positive plate and the electrolyte decays. This chemical change causes the internal resistance to increase. In time, the cell resistance raises to a point where the battery can no longer deliver the energy, although it may still be retained in the battery. Equipment requiring high current bursts is affected most by the increase of internal resistance.
Battery wear down on lithium ion polymer batteries is caused by two activities: actual usage or cycling, and aging. The wear-down effects by usage and aging apply to all batteries but this is more pronounced on lithium-based systems. The Lithium polymer batteries prefer a shallow discharge. Partial discharges produce less wear than a full discharge and the capacity loss per cycle is reduced. A periodic full discharge is not required because the lithium-based battery has no memory. A full cycle constitutes a discharge to 3V/cell. When specifying the number of cycles a lithium ion polymer battery can endure, manufacturers commonly use an 80 percent depth of discharge. This method resembles a reasonably accurate field simulation. It also achieves a higher cycle count than doing full discharges.
n addition to cycling, the battery ages even if not used. The amount of permanent capacity loss the battery suffers during storage is governed by the SoC and temperature. For best results, keep the battery cool. In addition, store the battery at a 40 percent charge level. Never fully charge or discharge the battery before storage. The 40 percent charge assures a stable condition even if self-discharge robs some of the battery’s energy. Most battery manufacturers store Li-ion batteries at 15°C (59°F) and at 40 percent charge.
Charge the Lithium ion battery often, except before a long storage. Avoid repeated deep discharges. Keep the lithium ion polymer batteries cool. Prevent storage in a hot car. Never freeze a battery. If your laptop is capable of running without a lithium ion polymer battery and fixed power is used most of the time, remove the battery and store it in a cool place. Avoid purchasing spare Lithium ion polymer batteries for later use. Observe manufacturing date when purchasing. Do not buy old stock, even if sold at clearance prices.