[grahame]

These cameras take D-LI109 battery and Pentax makes adapter for AA batteries and stated in the manual that these cameras take AA batteries as well. A really good design.
What I am confused is: D-LI109 battery is labeled 7.4V, most rechargeable batteries these days are NiMh type and the typical voltage is 1.2v. So together, they provide only 4.8V, very far away from 7.4V. Many of us much have noticed that if we use regular AA rechargeable batteries on these cameras with adapter, in most case the low battery symbol shows on the screen real quick. -- I guess that is why: we need 6 AA batteries to reach 7.2V!

I wonder why Pentax allows both D-LI109 battery and 4XAA batteries to power the cameras.

Even worse: I measured the voltage of the original Pentax D-LI109 battery last night and found all of them measured around 8.35V when fully charged!

[Alex645]

What I am confused is: D-LI109 battery is labeled 7.4V, most rechargeable batteries these days are NiMh type and the typical voltage is 1.2v. So together, they provide only 4.8V, very far away from 7.4V. Many of us much have noticed that if we use regular AA rechargeable batteries on these cameras with adapter, in most case the low battery symbol shows on the screen real quick. -- I guess that is why: we need 6 AA batteries to reach 7.2V!

I am not an electrical engineer, but I know voltage is only part of the equation, and amperage is the other. Rechargeable AA batteries typically have lower volts but higher amps than disposable batteries. For flash units, I know this means faster recycling times, but shorter life per charge.

On page 48 of the K-50 owner's manual, it is stated, "If AA Ni-MH rechargeable batteries with a capacity of approx. 1000 mAh are used, the batteries may not last for very long. Use Ni-MH rechargeable batteries with a large capacity." In other words, the higher the mAh rating, the better.

On page 284 they have the following chart:

[grahame]

I am not an electrical engineer, but I know voltage is only part of the equation,

I know very little about electrical.

The NiMh batteries I used are all high capacity, 2500mAh and above. didn't help much. Camera still gives low battery sign even refreshed and recharged batteries are loaded.
Actually alkaline batteries that have 1.5v labeled work better than these high capacity NiMh batteries. I believe they have less than 2500 mAh, although I am not 100% sure. Also I measure the voltage of these alkaline batteries, they give 1.6-1.7V when fresh, and voltage drops when batteries are drained. When camera says low battery, the voltage of alkaline batteries typically have 1.4-1.5v, and can still be used on other device such as flashlight. that is why I believe voltage play important role here.

[stevebrot]

Battery voltages are part of the EXIF makernotes. So is battery charge state. I wonder if those reflect your concerns (charge state probably does). As for the NiMH vs alkaline capacity question, a comment of another recent thread suggested that NiMH may prematurely show significant discharge when compared to alkalines.

Godox XProC on Pentax: tests with my K3II, V6 II and other Godox equipment - PentaxForums.com


Steve

[grahame]

I guess the thing bothers me the most is: since the D-LI109 battery has 7.4V (8.4v actual measured), why would Pentax suggest using 4XAA batteries. I understand the space at the grip area is limited, and probably does not have space for 6 AA batteries, but maybe they can reshape the battery cell and make an adapter that holds 6X AAA batteries. IN this case, 1.2x6-7.2V, is much closer to required voltage.

[Not a Number]

Fully charged alkaline batteries are 1.5v. They quickly drop to around 1.2v and down to 1v. Fully charged NiMH batteries are 1.5-1.45v. In use they drop down to 1.2v but remain around 1.2v longer than akalines. So in use the "working" voltages between akalines and NiMH batteries are about the same.

[LensBeginner]

Battery voltage in rechargeable batteries varies greatly with the amount of charge... some sets of batteries I measured ranged from 4.4 (barely used alkalines) to 5.5 (Ni-Mh), no-load, dropping to 3-3.2 under load.

I was an enthusiast user of rechargeable AAs on the K100Ds, but now with more modern cameras I think lithium has definitely the edge... especially when it can make a 3+ years old K-01 (live view only!) work for ~400 shots in one day on one charge!

I also had an unpleasant experience with a friend's K-X, she bought it used and the original owner hadn't updated the firmware (which crucially solved an issue with batteries). I had to hook the camera up to a homemade regulater supply in order to load the newer firmware and make the problem go away. Imagine the thrill of flashing a firmware with clamps precariously gripping to the contacts inside the battery compartment, and wires dangling out of it!

[THoog]

The K-x does not use the D-Li109, only 4xAA batteries. The K-S2 cannot use AA batteries. The only bodies to use either were the K-r, K-30, K-50, and K-500. (Not counting external grips.)

I guess the thing bothers me the most is: since the D-LI109 battery has 7.4V (8.4v actual measured), why would Pentax suggest using 4XAA batteries.

You're kind of putting the cart before the horse here. Up to the K-x, all the low-end Pentax bodies were built around 4xAA batteries. Supporting 4xAA batteries was just a legacy feature from teh K-r on. Since Pentax supported AA batteries inside the body far longer than any other DSLR maker, and they stopped after the K-50, it's kind of a moot point.

Five volts is fairly standard operating voltage for digital electronics. Four alkaline cells in series is 4x1.5 = 6 volts, which the camera regulates down to 5. Four NiMH cells are generally enough at 4.8 volts, although I also remember the issues with rechargeables when the K-x first came out (Eneloops seemed to work, even with FW 1.00). As Not A Number said, alkaline batteries start with a higher cell voltage, but this drops fairly quickly; NiMH has a lower cell voltage, but it holds that voltage much longer, until the cell is exhausted. (This is known as the battery's "discharge curve".)

Then Lithium ion batteries came out, but their chemistry gives a nominal cell voltage of around 3.7 volts instead of 1.2 or 1.5 volts. One cell is not enough, so each battery has two cells in series, giving 7.4 volts, and the camera regulates it back down to 5 volts. There's nothing special about 7.4 volts - if you had 6xAA NiMH batteries, they might still be wired to give 4.8 volts, with two of the cells in parallel to provide more amps.

[LensBeginner]

The K-x does not use the D-Li109, only AA batteries. The K-S2 cannot use AA batteries. *snip*

...but I was saying that because I have a K-30 which can theoretically use both

BTW I have like 4 sets of Amazon Basics in various cameras/flashes etc., the white ones everyone was saying that they are rebranded Eneloops: b0110cks! they are the worst Ni-Mh I have, some of them barely reaching 1500 mAh when measured with the Refresh/Analyze cycle of the Maha Powerex.

[THoog]

I have like 4 sets of Amazon Basics in various cameras/flashes etc., the white ones everyone was saying that they are rebranded Eneloops: b0110cks! they are the worst Ni-Mh I have, some of them barely reaching 1500 mAh when measured with the Refresh/Analyze cycle of the Maha Powerex.

I think the Amazon Basics have gone through a few different suppliers/generations. I have some (white with the green leaf logo, not the green stripe) that are almost as good as my older Eneloops, but not quite.

Edit: But I don't think for a minute that they came from the same factory as "real" Eneloops of that generation.

[LensBeginner]

I'll bite and try the top-tier Ni-Mh from Ikea (the 2450 mAh Ladda model), which were said to be very good... I won't go broke for a single set

[FozzFoster]

Battery voltage issue: K-x, K-r, K30, k50, ks2.. D-LI109.. AA battery
These cameras take D-LI109 battery and Pentax makes adapter for AA batteries

The K-S2 cannot use AA batteries.

Damn, I was excited there for a moment.. :/

[grahame]

Damn, I was excited there for a moment

Sorry for the confusion.
the reason the that research/experimenting was, my k30 developed aperture block issue and can not keep the lens aperture open when shooting, and result in black image. And as many others reported, using AA batteries helps. The problem occurs only when D-LI109 battery is used. --- I am not sure if it is true, I have the feeling the the 8.4v I measured on D-LI109 battery is the reason for that issue. otherwise, why AA batteries are better?
So I am trying to find good AA batteries for k30. And because K-x and KS2 also have the same aperture block issue, I mentioned them together
And I run into this problem: AA batteries can avoid the aperture problem (maybe because the lower voltage), they don't last. so I am trying different types of batteries, such as Ni-Zn battery, 1.6v. and hope some batteries can provide just good voltage and power the camera for a good time without aperture issue.

[LensBeginner]

They don't solve the issue... there have been reports of the issue getting less severe or disappearing for a certain time, but the underlying problem remains.

If it's a magnetic issue, reducing the current passing through the solenoid could result in a weaker magnetic field, and in less attraction or faster decay of said magnetic field.

If it's a mechanical issue, a weaker magnetic field could still play a role: maybe the horseshoe-shaped iron piece moved too rapidly and jammed because attraction was too strong? or when the current was switched off there was some residual attraction which caused the piece to move unevenly and jam... who knows?

Another piece of the puzzle... some guy on the Italian forum managed to temporarily revive a K-something by moving a magnet up and down close to the body, in the place where the ACB is. Camera gets better for a day or so.

We still don't know why it works.

[h4yn0nnym0u5e]

I've a bit of experience specifying batteries for portable equipment, so here's my take... With modern electronics, usually operating at 3.3V or lower, the important thing should be total capacity, down to some terminal supply voltage. The start voltage shouldn't matter too much, as a decent DC-DC converter should be able to get just as much out of an 8V 1000mAh battery as a 4V 2000mAh one. It's a matter of the energy capacity (watt hours, or Wh), which in these cases is 8Wh.

I did a bit of superficial research and came up with this:

Battery	voltage	cells	mAh	Wh
D-Li109	3.7	2	1050	7.8
AA-Li	1.5	4	3000	18
AA-NiMH	1.2	4	1900	9.1
AA-MNO2	1	4	700	2.8

Note I've given "normal" alkaline AAs a pitiful voltage and capacity - this makes them fit the K50 manual table fairly well, and suggests the peak current draw during "normal shooting" is about 2A, which will clobber them in short order. Lithium and NiMH cells will cope much better, as they're designed for this sort of drain rate (not true of lithium coin cells, though...). If you get poor life from NiMH that's often because one cell has drained more than the others. I seem to recall that the AA holder activates a switch telling the camera to expect a different cell chemistry and set its low battery limit accordingly, probably 6V for the D-LI109 and 4V for AAs. The "playback time" figures suggest much lower peak currents in that operation mode, though higher average current. It can be very confusing...

The aperture solenoid may work better at higher supply voltages (as long as the battery can sustain the current draw), because it could be an exception to the "everything runs at 3.3V" rule, and be run more-or-less directly off the raw battery power rail.

Cheers

Jonathan