As you may know, all Pentax DSLRs except the K10D adopt the “AA battery solution”, that means that those DSLRs only accept single-use disposable or rechargeable batteries in either AA or CR-V3 format.
K10D is the first and the only Pentax DSLR up till now which uses proprietary Li-ion rechargeable battery, which is the right thing to do, IMHO, but indeed Pentax responded too late and too slowly as the infamous Pentax DSLR battery issue/problem has been dragged on for so long since September 2003 with their *ist D to even up till now, for the K100D. In fact, there are still numerous different K100D users who are yet asking the related questions from day to day for the annoying problems they have encountered. Here is a recent example, which, for the first time, I could see a more concrete and sensible reply from a Pentax staff:-
Indeed, whilst the reply from the Pentax representative is true and this guy was indeed brave and helpful enough to tell the truth (which is absurd, however, e.g., try not to use the LCD as far as possible if one uses NiMHs, or, use CR-V3s which the DSLRs are designed for and etc.)
So, if NiMHs actually work like this and degrade the DSLRs’ performance and reliability so significantly, what other *rechargeables* else could be used by those pity Pentax DSLR users? The only solution left is the Rechargeable CR-V3s (RCR-V3s), which are made with the Li-ion technology.
However, do note that Pentax do state in their websites and newer user manuals that RCR-V3s should NOT be used in their DSLRs, “due to the voltage characteristics”, as stated. Indeed, the true reason for why Pentax do not want their users to even try RCR-V3 is likely to be that there exist non-voltage-regulated RCR-V3s which output “raw” Li-ion voltage, at around 3.7 to 3.8V per battery, which is just too excessive for their DSLRs which are designed to work at 6V, nominal.
On the other hand, for all other RCR-V3 models which are regulated to the lower voltage range close to 3V, i.e., similar to what those disposable lithium batteries would give, I can’t see how there can be any problem. The possible remaining factor would then be about the "internal resistance" of the battery, which constitute the *overall* characteristics of a battery (actually not just the “voltage characteristics” alone, which Pentax mentions about only) . But as Pentax have never mentioned about that it is the different internal resistance which would cause troubles nor actually there is any big difference in value of it when compared against those disposable lithium batteries. Again, the true reason for the banning of all RCR-V3s should not be with this factor.
BTW, I myself was able to find a good pair of RCR-V3 batteries with a very good charger (except that it only charges one battery at a time which causes some inconvenience and requires more time for charging two), after I had with my *ist D for a year, when I still could not resolve the annoying rechargeable battery issue with acceptable performance results with any of my Panasonic and Sony 2100 mAh NiMHs with original Panasonic charger or another not-so-famous brand charger named “Super”, which also working in the “negative pulse” charging principle (which the charging voltage is monitored to see when a negative change in the charged battery voltage occurs).
The two most annoying things of the problem were that the camera’s battery indicator shows most of the time that the battery is half depleted (thus the purpose of the battery warning is defeated) plus the camera obviously works slower as compared to when CR-V3s were used. The slower AF was most obvious, which still holds true for my *ist DS and K100D.
Ironically, at that time before I found the ultimate solution, I did use quite some of the methods stated by the above honest and helpful Pentax customer support representative, in order to save battery power when I used my NiMHs! Yes, I know that I can use my DSLR without the LCD turned on, as we used to shoot film, but why this is needed for a *Digital* SLR? And why we are forced to use our DSLRs in a film SLR way?? And, why I needed to use a DSLR without a low battery warning???
In contrast, since I got my RCR-V3s, all the problems were resolved and my DSLRs (include *ist D, DS and the K100D) with RCR-V3s in them perform as good as fresh disposable CR-V3s, except for maybe yet a shorter battery life, but they are rechargeables, not disposable anyway. The battery indicator does show the battery status correctly and accurately and that the AF speed is the same, most importantly. Furthermore, RCR-V3 batteries have very low discharge rate (versus that very high rate of the NiMHs), the built-in flash recharges faster and the Li-ion batteries themselves are lighter, too. Wow, there are just so many advantages with my RCR-V3s!
So, here comes the Question
Okay, let’s now back to the original subject title:-
When Rechargeable CR-V3s (RCR-V3s) rated at 1100mAh used in Pentax DSLRs outperform the highest capacity NiMH rechargeables, say, those rated at 2500mAh to 2700mAh, do you know WHY?
And, do you know and do you know how come the DSLRs' performance and stability will be inferior when NiMH AA batteries are used when compared against Lithium batteries, no matter they are disposable or rechargeables??
Before going on, we can first learn about briefly how rechargeable battery works, here. Having the most basic concept in mind, now that we can proceed with something that are more technical.
First, Let's have a look at the datasheet of the Energizer 2500 mAh NiMH:-
In the “Rated Capacity” of the battery Specifications, it is stated clearly by Energizer that the 2500 mAh rating was measured with a load which drew current at 500mA continuously with the battery discharged down to 1.0V. To explain the “mAh” unit in practical sense, it can be interpreted that the 500mA current can run for 5 hours before the battery voltage drops below 1.0V, which is called the “Cut-Off Voltage”, below which the (weak) energy delivered will not be counted.
Essentially, the mAh is an equivalent measure of the amount of charge that can be stored in a battery. Do note that the total charge is not equal to the total energy, i.e., to know the energy, the voltage should also be taken into account. I shall explain this in more details following this article.
From looking at the discharge curve for the 500mA load, it can be seen that the initial voltage can be as high as 1.4V but the nominal voltage, which is the voltage which appears most of the time along the discharge curve is around 1.2V (this is specified in the Specifications too). So, the total *energy* (not power) delivered can be roughly calculated, without integrating on the curve over the time, is: 1.2V x 500mA x 5 hours = 3Wh, per battery cell. Note that this “rough” calculation does match with the 2500mAh rating specified, as 500mA x 5 hours is exactly 2500mAh.
Actually, for high drain electronics devices which demand large currents, the total deliverable energy will drop, according to the curves for heavier loads. To calculate the exact deliverable energy is actually not difficult, it is just the total area under the curve by integrating the voltage values with time and then finally times the current in Ampre, then it is the energy. Again, for rough calculation without involving any statistical summation techniques (as the curve has *no* formula, it’s by measurement), the nominal voltage can be observed from the curve and used for the calculation.
Just take the maximum load of 5000mAh curve for example, the nominal voltage has been pulled down to 1.1V and that the cut-off at 1.0V occurred after approximately 0.4 hour. Thus, the total energy delivered is 1.1V x 5000mA (i.e. 5A) x 0.4 = 2.2Wh, or the total charge is only 2000mAh. So, in this extreme case, it is only about 70% of the much lighter load which draws 500mA, with the same cut-off voltage at 1.0V.
We all know that DSLRs are high drain devices, plus the cut-off voltage at 1.0V is indeed totally *not realistic* for Pentax DSLRs, which should be 1.25V instead. Again, I will explain in more details for how this value can be checked out later. In the mean time, just keep this value of 1.25V in mind, which is the true cut-off voltage when NiMHs are used in Pentax DSLRs.
So, before looking at how the 2500mAh energizer will discharge and when my K100D will shut off when using these battery. First, we shall look at how my RCR-V3s discharge in my K100D:-
Initial voltage for a freshly charged RCR-V3 of mine is measured to be 3.4V with no load. Nominal voltage of each is measured to be 2.8V during the full use per charge, when loaded with a simulated load (which discussed more about this later). The cut-off voltage of the *battery itself*, with load, is measured to be around 2.5V, which is the same as the cut-off voltage of the K100D (again, this will be explained later for how it is found). In other words, the batteries already cut off themselves when the camera shuts off. Thus, every drop of the rated 1100mAh battery juice can be used. Thus, the total deliverable energy in the camera is 1100mAh x 2.8V = 3.08 Wh. Thus, two of the RCR-V3s means a total of 6.16Wh energy deliverable, in total.
Do note that the nominal voltage of 2.8V is 100% safe and fine for the Pentax DSLRs as the initial no-load voltage of disposable CR-V3 can be as high as 3.5V whereas the nominal voltage is rated as 3V, and actually is again something from 2.5V to 3V with a heavy load like the K100D, as seen in this Energizer datasheet and specifications of their CR-V3. Furthermore, in the above I have used the rated figure of 1100mA regardless of the current load. It is because for lithium batteries, the mAh will not be greatly affected as NiMHs do. To place safe, I have verified for this also. Just refer to the above CR-V3 datasheet again, it can be calculated that the total mAh figures for the four curves for the four different loading conditions are all around 3000mAh (which is the rated capacity of the battery), although for heavy load the nominal voltage will drop somehow practically (which means that less energy will be delivered, but the total charge usable will be the same). I won’t go further for the detailed calculations for these, though. But you can try it out yourself if interested, it’s not so difficult to obtain the results afterall.
Normally, I can attain 200 to 300 numbers of shots per charge with my RCR-V3s, regardless of the storage period. So, I take 250 shots as the figure. So, to calculate the average energy spent in each shot, the total deliverable energy stored in the pair of RCR-V3s can be divided by 250 first.
Here it goes: 6.16Wh / 250 = 24.64 mWh. With this 24.64 mWh energy, the camera performs all the tasks executed by the user. Some internal functions of the camera, especially for a DSLR, will eat away extra energy without the notice of the user, e.g., the driving of the CCD imager, LCD, ADC, IPU, CPU for general control function, memory card read/write (say, shooting RAW will use more energy), mirror up/down, aperture blade movement, and etc. Yet, other obvious "external" functions of the camera like AE metering and AF, or even the SR, still consume much energy.
So, with this 24.64 mWh, for each shot, if the DSLR does the job faster, more current will be drawn. On the other hand, if the camera does the job slower, less current will be drawn, but the time for completion of all the required tasks will be longer. I myself will not go further to measure the current nor the timing per shot for my typical usage pattern which actually would require a power analyser which can measure the current in ampre (and all other parameters like voltage, resistance and dissipated power as well) and plot it over the time (of course conduction wires are required to connect in between the camera and the batteries, in series, as the analyser is now an ammeter). So, to make the case simpler, here is a best estimate on the average time required per shot for my usual shooting habit / operation sequence:-
Setting the camera for 5 seconds; AF and AE another 5 seconds, take the shoot for 1 second, instant review for 3 seconds (as set as default), playback review for 5 seconds, plus, other camera's delay in processing and memory card read/write: another 3 seconds => total time required is equal to: 22 seconds.
So, we can now estimate the *average* current consumption of the K100D, we can divide the energy by the nominal loaded voltage and then by the time in hour, i.e.: 24.64 mWh /5.6V / ( 22 s / 3600 s/h ) = 720 mA.
And hence, the *average* resistance of the K100D is estimated to be 5.6V / 0.720A which is equal to 7.78 Ohms.
Now, if we are to compare the NiMH performance, to be precise, we can use this resistance value of the K100D. The practical implication of such a resistive load is that it will draw less current for a lower voltage applied. As for the energy spent or the work done for a particular job, they should be similar, e.g., work done (energy used) by the AF motor, a lower voltage means less current and thus the same job will require more time to complete (as the total energy spent / work done is roughly the same), thus, it is doing the same job comparatively slower just because the power is lower. This actually explains why AF is noticeably slower with NiMHs than with lithium power sources. For those who haven't noticed the difference, just put on the lens cap and half press the shutter release button and just let the AF motor to focus the lens to and fro and the difference in speed between NiMHs against Lithiums can be observed .
Now, we can look back again at the discharge curves of the Energizer NiMH. So, the first thing is that we should decide on which discharge curve is closest to the case of the K100D for the amount of the current drawn. So, the calculation now is possible with we get the estimated resistance of 7.78 Ohms. Hence, the current can be calculated as 5V / 7.78 Ohms = 643 mA.
Well, now I am going to tell why I could use 5V as the total battery voltage in the above. Still remember the cut-off voltage discussed above (for the camera itself but not the battery)? Here is an easier way to measure the cut-off voltage of the K100D: Just shortly after the K100D with NiMHs cut-off and shows battery depleted, pick out the batteries and measured the voltage with a close enough low resistance load with the batteries (ideally should be 7.78 Ohms for four NiMH batteries, mine is of 4.75 Ohms, so I loaded two batteries with it only) and the on-load output voltage is measured. I thus was able to find out that the K100 is very sensitive to the 5V border line. I do the same for my both my CR-V3s and RCR-V3s, with my load on each battery, and still I got a close figure to 2.5V per battery, thus, it is of 5V again for two (R)CR-V3s!
For NiMH batteries, a 5V cut-off in the camera simply means a 1.25V cut-off voltage per battery cell. Do note the 1.25V is indeed a higher value than most typically rated nominal voltage of NiMHs (whereas some others are yet rated at 1.25V nominal) and this doesn’t make much sense at all for such a high cut-off voltage required (but I bet the Pentax engineers had no choice, as the power requirements of their DSLRs are so high – so that a further lower voltage may not be feasible for the circuitries and electronics inside).
With the cut off voltage border line at 1.25V in mind plus an estimated drawn current of 643mA, we can now choose which discharge curve to look into. The 500mA discharge curve is close enough, although it's still slightly lighter for the load. Now we can check *when* do the cut-off of 1.25V will take. It can be seen that it can last for just a little bit over 2 hours without touching the 1.25V line, according to the curve, i.e., the flat part of the discharge curve (shortly after 2 hours, it starts to fall).
So, the total deliverable energy for the “2500mAh” NiMHs (before the camera cuts off) is: 5V x 500mA x 2h = 5 Wh.
Now, remember how much energy is deliverable for the two RCR-V3s? It is 6.16Wh. So, even having give the advantage to the NiMHs for the lightest load of 500mA (amongst all the tested loads in the datasheet), the "1100 mAh" Li-ion RCR-V3s still outperform the "2500 mAh"NiMH AAs.
Indeed, the fact is that even before the cut-off, the NiMHs provide a low voltage which the camera is *always* working very near the border line and this is undoubtedly the stability of the camera is affected. Indeed, the battery indicator does tell this very clearly (as it won’t lie) and the half-depleted warning does often show up. Do note also that if the battery voltage just drops below the border line for incident, the camera will shut off. Despite that there might be some juice left, which could still be sucked out bit by bit after enough “resting” time is given to the battery (to wait the battery voltage to come up again). However, I think this is indeed impractical in the field. Under normal circumstances and practically, when the camera is shut off for the first time, the user will surely replace the rechargeables immediately, I bet!
To consider an even more practical factor, do note that NiMHs are actually the fastest self-discharging rechargeables in this planet. So, after storage of the battery for a few days, I’m sure that you cannot get anything near the ideal value of 5Wh calculated above, neither.
Until very recently, Sanyo and GP have been able to develop and market their new NiMH batteries called Eneloop and ReCyko+ respectively so as to tackle with the annoying fast self-discharge problem of the NiMHs. Despite the storage time will be lengthened without significant loss of charge over time, the output voltage of those batteries are still at 1.2V nominal, as the chemical used in the batteries are still NiMH. Also, the rated capacity is smaller now at around 2000mAh for both. From what I have heard, those new batteries seem to have a flatter discharge curve which might be more favourable to the Pentax DSLRs, for the killing weakness mentioned above. But still, the cameras are still working near the border line and the performance of the camera is greatly affected, even you use Eneloop, here is an example.
In addition and finally, do note again that the typical 2500mAh NiMH rating is measured based on a quite ideal operating temperature of 21 deg. C (general room temperature) and minimal load condition. With the further decrease in temperature, e.g. shooting outdoor in winter, the total energy delivered will be decreased further accordingly. And as we all know, Lithium-type batteries are superior for cold temperature and for heavier duty whereas liquid type batteries like NiMHs and Alkalines are rather susceptible for lower temperatures. Here is a comparison between the performance of Lithium and Alkalines AAs for how they could differ.
Indeed, I found that my K100D is just more power hungry than my *ist DS which is again more power hungry than the *ist D. The symptom is that the power is cut off faster for the newer than the older, which simply implies either the set cut-off voltage had been raised for each newer model or it would be the case that the power juice is drawn faster for the newer camera, even the cut-off voltage set is the same.
In real practice, I find that the only usable NiMH batteries of mine in my K100D now is the Sanyo 2500 mAh NiMHs, which can shoot less than 100 pics for my shooting style per fresh charge, and must be within just a few days, whereas my RCR-V3s are typically good for around 200 to 300 shots per charge, regardless of the storage period, as I have already mentioned above. The practical results agree in general with all my calculations and measurement described above, which are largely based on the detailed data and information contained in the battery datasheets.
Well, for the K10D, I do bet, which is the latest model with the most powerful specifications of a Pentax DSLR ever, maybe even more power hungry than the K100D and thus it is very possibly that it is completely not viable to use the “AA battery solution” anymore. The “AA battery solution” in Pentax DSLRs was and is indeed a totally wrong decision by Pentax from day one and is simply a design fault, frankly speaking. I don’t know if it was a marketing decision which overruled engineering judgement or not, but undoubtedly, the outcome was indeed terrible.
To make the situation even worse, Pentax’s official “ban” on *all* the RCR-V3 batteries instead of compiling a Tested & Approved list of those which are actually working ideally in their DSLRs (which actually unleash the peak performance and ultimate stability of their DSLRs, instead, ironically), was and still is, another very wrong decision, which Pentax missed the boat again for an actually viable remedial action for their original wrong decision (and wrong design). The sad consequence is simply that most Pentax DSLR users have no reliable rechargeable batteries, of any type, which is also officially approved by Pentax, that they can feel safe to use in any of their “AA battery solution” DSLRs, nor the DSLRs are actually operating at their optimal performance, which originally they are capable of !
I really hope that similar tragedies won’t happen anymore to Pentax (and actually more to their users) in the future. *If* Pentax *could* really listen to their customers, admitted problems and reacted promptly and positively, they could have been a more successful company in the market, instead of struggling for survival like what they are doing now. Nevertheless, ideally, they should have prevented stupid problems from happened at the first place, honestly speaking (although they hadn’t for this case).
Update (on March 4): Since I have been bashed by particular die-hard blind brand loyalists who are "very happy" with their AA battery DSLRs, since I published my this article and everything became personal in the end, I feel very obliged to point to some feedbacks of other Pentax DSLR users who have reported about the problem. Indeed, those reports appear extensively from day to day and are very easy to find. In the end, even those people who bashed me didn't/couldn't see any problem themselves, why they needed to stop others from reporting the problem and also needed to put hatred on me for what I had looked into the case and suggested a possible solution here?
To illustrate it is not an isolated case nor it is "the user's problem", I simply choose a recent thread at the Dpreview forum. It can be seen that there are so many different users who are desperated, upset and reporting the true experiences of their "own" case(s), just within such a single short thread. I opt to list out some of the relevant reporting posts below:-
Also, this user is right to the key point, for the sluggish AF as a result of low voltage owing to the use of NiMHs:-
It's very obvious that there exists a common problem of the "AA battery" Pentax DSLRs and that Pentax's customer support staff seem have no much to do and can do for helping the customers who approached them for the problem. For that those users who have found and reported the problem are being accused of having problems themselves instead (by those blind brand loyalists) is actually utter nonsense. And, for those who try every effort to bash a person who is actually trying to be helpful is indeed very silly, again. Afterall, for all those blind brand loyalists who always like to respond to me in a personal way would not help anyone, including themselves nor their blindly loved brand, I must say. I do bet that the only "achievement" they could attain is that they could possibly feel much safer and more comfortable psychologically themselves by (always) doing so.
All in all, I have never rejected the possibility of some users are "okay" with their *particular* AA battery Pentax DSLRs with their *particular* AA batteries in them, for their **particular** applications (e.g., there exists an user who have responded that he could use his Pentax DSLR with AA Alkalines with no problem, really amazing!). Yet, there is an issue, in general, undoubtedly!
Friday, March 02, 2007