Saturday, August 28, 2010

Battery - FAQ

This FAQ sheet was designed with the help of Battery University, which is a major source for the content within. Where technical data requires preservation or otherwise lengthy explanations, hotlinks will be provided. Permission has been obtained from Battery University (Isidor Buchmann) to use their copyright material in creating this FAQ sheet.

Battery myths – are all batteries created equal?
Unfortunately no! Batteries are not created equal, regardless of what some folks may say or proclaim. To further exacerbate this dilemma, batteries from the same manufacturer often differ from one another due to poor or non-existent quality control. This has been observed in both length and girth, causing endless frustrations within the vaping community.

What do the numbers mean on a battery?
In general the numbers relate to the battery size in mm (millimetres). The first being its diameter, the second its length. The fifth is to indicate single cell. For example: an 18650 battery is 18mm in diameter with a length of 65 mm.

Another number found on batteries is the “mAh” rating (milliamp hour), which equates to the amount of stored energy in the cell. The higher the number the higher the potential energy available to be converted into work (vaping in our case) by the end user. This figure expressed in mAh is usually directly related to battery size, but not always. It is indeed possible to have 2 different size batteries with the same “mAh” ratings but the similarities end there.

What's the best battery?
In my humble opinion, folks should purchase the best battery they can afford. I am partial to the AW line for quality, durability and consistency. Not all batteries are created equal, and hence my battery of choice is the AW line. Why?

Because AW's quality control and assurance is second to none in the industry in my opinion. When it comes to battery safety, they have gone one step further than many only attempt to achieve.

Should I buy protected or non-protected batteries?
This again is a highly subjective topic, with an even more difficult answer. One should only buy protected batteries, whether or not they are intended for use in series or as singular cells. Why?

Some may argue that the protection is only as good as the life of the PCB (printed circuit board) and, like any other electronic component may fail pre-maturely. Although the latter is unquestionably true, the added measure of safety cannot, in my humble opinion, be so readily dismissed or refuted for that matter. The anatomy of a Protected Battery

What battery do I need for my device and/or which one should I use?
It has now become customary for vendors to list their recommendation with regard to which batteries to use with their particular device. This wasn't commonplace not too long ago, but is now becoming the norm. The latter becomes paramount with some of the newer “all mechanical” devices. Why?
Because some of the newer “mods” are being fabricated to close tolerances and many no longer use springs in their devices, to compensate for varying battery lengths. To further exacerbate this problem, batteries from the same manufacturer do indeed have differing lengths of the same battery. Why?

We don't know, but please do not solely rely on the manufacturer's quality control process, as you will be sorely disappointed. When in doubt, use the vendors approved and recommended battery/ries.

Battery chargers – which one should I use?
Once again, use the one recommended by the vendor or better yet, the battery manufacturer. When in doubt, follow the manufacturer's recommendation. There are several “multi-chargers” on the market that perform well and are indeed endorsed. I would suggest buying one of these if you are using different battery sizes in your devices. It makes absolutely no sense to use multiple chargers when one will do.

What should be the charging capacity of the charger?
Depending on which battery the charger is called to charge; it needs to be charged to the appropriate voltage. e.g. 4.2Volts for 3.7V nominal or 3.6V for 3V nominal. Although you can use a lower capacity charger with a higher capacity battery (voltage), doing the opposite could lead to catastrophic failure of not only the charger, but the battery as well. This failure has the potential to degenerate into very serious consequences, to include but not limited to: battery venting, explosion and fires. On the other hand, using a charger intended for 3V batteries will result in a 3.7V battery being undercharged.

Can I charge batteries with different chemistries on the same charger?
Providing the charger is designed to charge the specific voltage of the battery being charged, then the answer is yes, as the charger does not care about the chemistry. However, it is not recommended to charge batteries with dissimilar chemistries simultaneously e.g. on a multiple channel charger. This ensures an added measure of safety.

Battery chemistry – is there a difference?
Yes there is, and a significant behavioural difference in both safety and general use.

What is the difference if any between the different battery chemistries?
Lithium Ion (Li Ion) requires a protection circuit for safety, whilst Lithium Iron Phosphate (LifePo4) and Lithium Manganese (LiMn or IMR) use safe chemistry. Although these batteries utilize safer chemistry, protection circuits are generally recommended. The safer chemistry will prevent venting with flames in the event of a catastrophic failure, whilst LI Ion batteries contain and oxidizer, which produces its own oxygen to support combustion, should sufficient heat be available at the source. Lithium-ion safety concerns
Furthermore, the LiMn or IMR battery is capable of handling greater load demands than their cousins the Li Ion and LifePOs (in a much smaller package), and hence is commonly referred to as a “high drain” battery. Providing the battery has the appropriate C rating for the application, these are the recommended batteries intended for use with low resistance atomizers.

Notwithstanding, larger cell Li Ion batteries are indeed capable of meeting large load demands. In these instances, battery longevity between recharges becomes the deciding factor between the two. e.g. The AW 18650 2600mAh battery will outlast the IMR 18650 1600mAh battery:
  • IMR18650 1600mAh 10C :
  • (1.6*10) = 16A for 6min; whilst
  • AW 18650 2600mAh 2C
  • (2.6*2) = 5.2A for 30 min
When using a factor of 3 against the IMR, (16A/3) = 5.3A in can readily be seen that decreasing its load demand will not increase its longevity significantly (6min *3) or 18 minutes, when compared to a similar load handled by the standard 18650 for 30 minutes. This data backs up speculation that IMRs are effective in all cells, where it can be clearly seen here and, as experienced by the community that IMR chemistry is wasted in larger cells. When using the mathematical equations, greater battery longevity is achieved using a standard 18650 over the IMR battery. In addition, IMR cells are unprotected. Although IMR cells use safer chemistry, the use of protected batteries should always be the deciding factor in which battery to use when, the increase workload capacity is of inconsequential value.

What does stacking mean?
Stacking is a slang term used to describe connecting the negative end to the positive end while using two or more batteries. The correct term would be connecting batteries in “series” or, using the batteries in “series”. When connecting your batteries in “series”, you are doubling the voltage while maintaining the same capacity rating (amp hours).

What does parallel mean?
Unlike in “series”, in “parallel” means connecting the positive end of one or more batteries to each other while connecting their respective negative ends together as well. When connecting in “parallel” you are doubling the capacity (amp hours) of the battery pack while maintaining the voltage produced by a single cell. e.g. many hands make for light work.

Are there advantages in using batteries in parallel over using batteries in series?
Yes. The main advantage in using batteries in parallel is, the capability of the batteries to do the work a single cell would prove incapable of doing. Connecting in parallel ensures the workload is shared amongst the cells connected to each other and not overstressing any cell in the circuit. An example using a 14500 900mAh Trustfire battery (The *** fire series battery has a C rating of 1.5):
  • This single cell is capable of doing (900mAh/1000)*(C or 1.5) or 1.45A worth of work;
  • The demand on the battery is 1.6A from an average 2.2 Ohm atomiser. As the battery can only produce 1.45A, the battery will be stressed when current is drawn from the load.
On the other hand, should we connect 2 or more cells in parallel:
  • (1.45)*2 or 3 = 2.9 or 4.35A We now have sufficient power available to adequately meet the work load of 1.6A, without stressing any of the batteries in the circuit.
If I stack my batteries can I achieve similar results?
No. Because amperage draw is a relation between voltage/divided by resistance or I=V/R. As previously discussed, when we connect our batteries in series we effectively double our voltage while keeping the battery capacity (mAh or I) to do work the same. Once again our 14500 3.7V 900mAh battery:
  • This single cell is capable of doing 1.45A (900mAh/1000)*C worth of work;
  • should we double the voltage (3.7*2) = 7.4V;
  • applying the formula I=V/R or (7.4/2.2) = 3.36A The workload is nearly 2.5 times greater than the carrying capacity of the “stack”, resulting in a seriously overstressed and potential catastrophic condition, especially if unprotected batteries are used.
Is there a way to use this battery pack effectively? Yes, by increasing the resistance of the atomiser used in this application.
  • If I=V/R then R=V/I or (7.4/1.45) = 5.13Ohm.
What is “C” rating when referring to batteries?
“C” rating is simply a way of talking about charge and discharge rates for batteries:
  • 1C = 1 time the rated mAh capacity of the battery. So a 900mAh battery at 1C can discharge 900 milliamps, or 0.9 amps for 1 hour. Most batteries, unless specified, have a C rating of 1;
  • 1C for a 2600mAh battery would equal 2.6 amps for one hour; whilst
  • 2C for a 2600mAh battery would equal 5.2 amps for 30 minutes from 1 hr.
As seen, while the C rating can effectively double the working capacity of a given battery, it also reduces the effective time the battery has of working at the increased load. The opposite holds also true when using “fractional C”:
  • while 1C for a 2600mAh battery can produce 2.6 amps for one hour;
  • 0.5C for a 2600mAh battery equates to 1.3 amps for 2 hours, effectively doubling battery run time but decreasing the current being applied to a given workload.
Why do we need to keep our batteries in pairs?
Because metaphorically speaking, teams that are used to working together perform better. That being said, in battery usage we are trying to keep the internal resistance of the batteries the same, or as close as we can get them to each other.

What is internal resistance in a battery and where does it come from?
Lithium-ion batteries lose capacity through cell oxidation (cholesterol), a process that occurs naturally during normal battery use and aging. As the battery ages, internal resistance (cholesterol) increases as well. This increase in cholesterol (internal resistance) leads to plaque build up and when sufficient build up occurs. This results in a plugged artery/battery or, a battery that can no longer deliver current sufficiently to meet the workload. Not dissimilar to someone having a heart condition having difficulty going up a flight of stairs.


Does internal resistance decrease the amount of usable energy in a battery?

Yes it does. It reduces the battery's overall charge capacity. Three imaginary sections of a battery consisting of available energy, empty zone and rock content. With use and age, the rock content grows.


I have heard a term “stressing a battery”. What, if any, effect does stressing a battery have?
The short answer is rapid ageing due the increase build up of cholesterol (or internal resistance), in this particular case caused by excessive work demands. These excessive work demands increase the creation of internal resistance (cholesterol) exponentially, leading to an increased plaque build up (the rock zone).

Is stressing a battery dangerous?
Yes, emphatically so.

What could be the results of a stressed/over-stressed battery?
In milder cases, the build up of plaque results in a plugged artery and possible heart failure, or in our case the battery will no longer hold a charge or deliver current.

In severe cases clogged arteries can lead to aneurisms and death. In our application, should the protection circuit fail, and we have a stressed battery, which translates to an over-current condition, the battery may vent or even explode.

Keeping our batteries in pairs, why?
As seen in the previous discussion, internal resistance in batteries reduces the ability of current to flow. Should one battery contain greater internal resistance than the other in the pair, that battery when called upon to work, will exert itself at an X factor compared to its counterpart. This increase exertion (in trying to keep up with its counterpart) will lead to an increase in internal resistance. As time goes buy, the internal resistance grows exponentially until battery failure occurs.

Because electrical current flows in a closed system, the battery with the lesser internal resistance is trying to push a golf ball through a garden hose (so to speak). This in turn causes an increase in internal resistance of the “good” battery. As the internal resistance in the “good” battery increases, the battery containing the greater internal resistance is stressed even more, once again increasing its internal resistance due to work. Why? Think of it as trying to fight your way through a jungle using a machete when compared to a walk in the park. Which one is less demanding?

How do I ensure my batteries are kept in pairs?
They are normally received from the manufacture that way. Once received mark the pair with a letter and a number e.g. A1 and A2.

Is the number important and if so why?
Yes it is. A natural phenomenon takes place in a stack that many cannot explain. The battery closest to the load will discharge quicker than its counterpart. Many theories have materialized over this, but for all practicality, we know it occurs and will leave it at that (in this discussion). You should alternate your batteries in subsequent uses. e.g. If A1 was used on top, A1 should be used on the bottom next time the set is used, and back on top for the following use, and so on, and so on... This will insure a greater distribution of the workload and a more natural and even build up of internal resistance, extending overall battery life. Think of it as rotating the tires on your vehicle, wearing them out evenly.

How many batteries should I purchase?
This question carries many possible answers based on specific demands the batteries will be subjected to, dependant on the vaping lifestyle of the end user, battery capacity, and whether the battery is to be used as a single cell or in series application.

Generally speaking 3-4 batteries should suffice in meeting daily demands in single cell applications, with this caveat. The 10440 battery does not have the carrying capacity (320-350 mAh) of other batteries. In this instance I would recommend acquiring at least 6 even 8 cells.

On the other hand if the batteries are intended for use in series, then one would need a minimum of 2 to 3 sets or 4-6 batteries to adequately meet vaping demands.

Is there such a thing as battery maintenance?
Yes, but perhaps not what one may think in terms of maintenance perse, but proper battery care. Battery care consists of:
  • keeping the cells clean at all times;
  • store your batteries in protective cases, inn a clean dry area;
  • if a protective case is not available, batteries should be stored flat in such a way to avoid having their contacts come into contact with each other. Protective cases ensures the latter;
  • daily inspection of its protective covering to reduce the possibility of “shorts” occurring. The latter is paramount for batteries with an intended use in metal tubes, or all metal devices, where the container is used as the negative pole to carry current;
  • batteries should be numbered and used in rotation. This will ensure batteries wear evenly;
  • when first receiving the batteries, they should be placed on the charger, and charged. Many batteries will come from the manufacturer charged. However, this voltage is known as residual voltage and although it may indicate the available voltage, it does not indicate the state of charge of the battery perse, or how long the battery has seen a fresh charge. There is no need to break in a battery so to speak, this myth has been debunked. You do not need to charge a new battery for 8 hours or even overnight. A charge until the light on the charger turns green is more than sufficient;
  • always check the voltage of the batteries coming off the charger. This will indicate not only the state of charge of the battery, but also how the safety cut-offs of both the battery's PCB and charger are working. Should an over-charge condition exists, one should investigate the cause of the over-charging condition before continued use of either the battery or charger;
  • once the battery has quit performing or has met its low voltage threshold (caused by the safety feature of the battery's PCB) check the residual voltage of the cell prior to placing the battery on the charger. It is also important to make note of how long the charge cycle lasts until the light on the charger turns green.
This data is important for future reference as:
  • it will indicate the state of the battery's wear. One can expect a shorter charge cycle as the rock content of the battery builds with use and age, but also the state of the charger itself; and
  • if for unknown reasons, should the charge cycle take longer than what was the “norm” for that specific battery, the cause should be investigated. A faulty battery's or charger's protection circuit may be at fault or both. If anything, as batteries age through use, it should take less time in subsequent charges to bring the battery to full charge, as the storage capacity of the cell has been reduced by the increase rock (cannot store energy) content of the cell.
Keep notes of run time and charge times. As a battery wears, its run and charge cycles are greatly decreased, whilst it charge intervals greatly increase. These are clear indications that a battery’s usefulness as come to a head. Time to order new batteries.

How does one measure voltage?
By using a multi-meter. A digital multi-meter is recommended over the analog type, for accuracy alone. Multi-meters are not simple voltage checkers, they come with the capability to check resistance amongst other things. Every home should have one of these as its use far extends beyond vaping

Why do I need one?
An ECF member has a quote in his signature. “A vaper without a multi-meter, is like a Doctor without a stethoscope”. In my opinion no truer words were ever spoken. Proper usage of this tool not only adds an added measure of safety, but also can be used to detect problems on the horizon before they actually occur or could have otherwise gone undetected.

As previously mentioned above. Judicious daily use of a multi-meter in battery monitoring, will often lead in avoiding possible accidents. The multi-meter is a way of checking the health of not only batteries but that of atomizers as well. Not only can it check for their state of health, by measuring their resistance, it ensures the proper atomiser is utilized with the intended voltage to be used. As all atomizers look alike unless specifically marked by either the manufacturer or the user, the use of a low resistance atomizer at high voltage would lead to its demise rather rapidly.

Furthermore, some atomizers will see their performance decrease over time and that is a good indication that the atomizer's days are numbered. Often, the atomizer will quick working for no known reason. A quick check on the multi-meter will tell us immediately if the atomizer is in fact dead, or their is another underlying problem. Sometimes a given atomizer works well on one device but not on another. Once again a quick check will narrow down the culprit.

How does one ensure safety when charging batteries?
  • first and foremost only used a charger designed for that specific battery. When in doubt, always follow the battery's manufacturer's recommendation;
  • never charge batteries unattended or overnight;
  • monitor charging. If the battery/ies or charger become unnecessarily hot ((read hot not warm, warm = OK, hot = NOT) (and warm is defined as slightly warm)), unplug the charger immediately, and remove the battery/ies from the charger, and investigate the cause;
  • charge batteries away from any flammable material, especially non protected LI Ion batteries. Although more folks are turning onto protected batteries, many still purchase un-protected cells. I believe this practice will continue for as long as manufacturers continue to make unprotected cells.
It is not recommended to charge:
  • batteries with differing chemistries simultaneously on the same charger;
  • it is not recommended to charge batteries with dissimilar voltages on the same charger. As a matter of fact, when it comes to voltages, only use the appropriate charger to charge batteries;
  • it is not recommended to charge same size batteries but with different “mAh” ratings together on a multi-channel charger simultaneously; and
  • it is not recommended to charge batteries from different manufacturers on the same charger at the same time.
  • Always charge batteries used in sets, as a set, and always charge batteries used in single applications as a single;
  • always remove batteries when the charger's light turns green. Batteries do not require a trickle charge, this is a practice that not only is unnecessary, prolonged charging will only result in a diminished lifespan of the cell itself;
  • should one battery charge quicker than another remove the battery from the charger. Take note of this, as this is an indication that either the battery's internal resistance is greater than the other battery in the set, or that that particular battery was depleted further than its counterpart. Although, it is normal for batteries from the same set to charge quicker than one another, large discrepancies in charging times are to be treated with caution. As once again the batteries and or charger could be at fault. A quick cheek prior to charging should have indicated this, if not change channels during next re-charge and see if indeed it is the battery or the charger's channel that may be charging slightly slower. Should upon investigation it be proven that the battery is at fault, the use of that particular set should be relinquished to single cell use, and in the case of 3V cells (which are useless for single use applications) the set disposed of;
  • however should it be proven that the charger is or may be charging at different rates between channels, it is then advisable to think of replacing the charger;
  • never charge a battery that has been depleted passed its low voltage cut off. One may be able to charge a battery successfully. This shall only occur under close scrupulous supervision. Any indication of a problem, cease charging immediately and dispose of the set, or relinquish the remaining battery to single cell use. Never, ever introduce a previously used battery from one set into another and, never mix an old battery with new ones to form a set. Batteries form a set, are used as a set and are disposed of as a set, or one is relinquished to single cell use, if this is deemed cost effective e.g the battery is fairly new. In all other cases, dispose of, as a set.
What are the different battery specifications for the AW line?


IMR 26500 Specifications:
Capacity : 2300mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 5A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 20A
Operating Discharge Temperature : -10 - 60 Degree Celsius
Size : 26.20mm ( diameter ) x 50.40mm ( height ) +/- .05mm

Special notes:
  • There is no specific charger for these batteries. We recommend the Ultrafire WF-139 charger used with magnets to make contact;
  • These are flat top cells - cell to cell contract requires slight pressure ( tail cap spring of a Mag will provide sufficient pressure ). DO NOT use a magnet in between cells to avoid ' shorts ';
  • Fitting in a Mag C is snug / airtight depending on the body version. Please check inside body tube diameter before purchase. You may need to sand the inside of the body tube of the Mag C to enable these cells to slide in/out freely.
Caution:
  • Do not over-discharge/overcharge;
  • Recharge empty batteries ( resting voltage ~3.6V ) as soon as possible. Leaving LiIon batteries in discharged state will incur irreversible damage ( capacity / cycle loss );
  • Do not short circuit ( will release tremendous current );
  • Do not dispose of in fire.
Attention: These IMR cells have much lower internal resistance than regular LiIon 3.7V cells and they may end up with a higher ending voltage when charged in certain chargers ( especially older version WF-139 charger ). Please check the voltage of them right out of the charger to see if they are above 4.20V when fully charged with your charger. Overcharging above 4.25V may shorten life/cycles. Above 4.50V may even pop them or making them leak. DO NOT use the charger if it seems to overcharge IMR cells.


IMR18650 Specifications :
Nominal Voltage : 3.7V
Capacity : 1600mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 4.5A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 10C
Operating Discharge Temperature : -10 - 60 Degree Celsius


IMR18500 Specifications :
Nominal Voltage : 3.7V
Capacity : 1100mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 3A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 8C
Operating Discharge Temperature : -10 - 60 Degree Celsius


IMR16340 Specifications :
Nominal Voltage : 3.7V
Capacity : 550mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 1.5A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 4A
Operating Discharge Temperature : -10 - 60 Degree Celsius


IMR14500 Specifications :
Nominal Voltage : 3.7V
Capacity : 600mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 1.5A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 4A
Operating Discharge Temperature : -10 - 60 Degree Celsius
Size : 14.07mm ( diameter ) x 48.80mm ( height ) +/- .1mm

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AW 18650 - 2900 Specifications:
Nominal Voltage : 3.6V
Capacity : 2900mAH ( rated at 0.2C discharge 4.2V - 2.5V @ 25℃ )
Operating Temp. : Charge 0 to 45℃ / Discharge -20 to 60 ℃
Recommended Charge Rate : 825mA ( ambient temp. 25 ℃ )
Max. Discharge Rate : 5.8A ( ambient temp. 25 ℃ )
Dimensions :18.52 X 68.16mm ( +/- 0.3mm )



AW 18650 Specifications:
Constant Voltage : 3.7V
Capacity : 2600mAH ( rated at 0.2C discharge 4.2V - 2.8V @ 25℃ )
Operating Temp. : Charge 0 to 45℃ / Discharge -20 to 60 ℃
Max. Charge Rate : 2.6A ( ambient temp. 25 ℃ )
Max. Discharge Rate : 5.2A ( ambient temp. 25 ℃ )
Dimensions :18.52 X 68.16mm ( +/- 0.3mm )


LifePo4 RCR123 Specifications :
Nominal Voltage : 3.2V
Capacity : 500mAH
Lowest Discharge Voltage : 2.0V
Standard Charge : CC 250mA CV 3.6V
Cycle Life : > 500 cycles


AW RCR123A Specifications:
Nominal Voltage : 3.7V
Capacity : 750mAH
Lowest Discharge Voltage : 2.50V
Cycle Life : > 500 cycles
Max. continuous discharge rate : 2C
Overcharge protection at 4.35V
Over discharge protection at 2.45V
Short / over-current protection
Operating Discharge Temperature : -10 - 60 Degree Celsius
Size : 16.62mm ( diameter ) x 34.29mm ( height ) +/- .1mm

Bibliography: Battery University
Battery University is an on-line resource that provides practical battery knowledge for engineers, educators, students and battery users alike. The papers address battery chemistries, best battery choices and ways to make your battery last longer.

Permission was obtained from Battery University (Isidor Buchmann) to use their copyright material in creating this FAQ sheet.

We are all concerned about safety and I herewith give you permission to use the material of Battery U for this purpose. More information will be released as part of the 3rd edition of "Batteries in a Portable World," material that will make its way to Battery U.

Good luck,

Isidor Buchmann
Cadex Electronics Inc.


Links of interest at Battery U.
Is lithium-ion the ideal battery?
The high-power lithium-ion
Lithium-ion safety concerns
Serial and parallel battery configurations
Charging lithium-ion batteries
How to charge - when to charge table
Discharge Methods - C rate
Internal battery resistance
The battery fuel gauge
Storing and priming of batteries
Do and don't battery table
The Secrets of battery runtime
Non-Correctable Battery Problems
How to prolong lithium-based batteries
Battery performance as a function of cycling

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