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Maintainance of CMOS or memory or backup-battery
Posted By: photogem, 06-10-2021, 01:53 AM

We have many threads here about problems with the socalled back-up battery (memory battery)

One could also call it "CMOS-battery:


This tiny battery, a Lithium 3V Seiko MS414 is located on the motherboard of your Pentax exept the very first *ist-D which had it in a tiny compartment on the bottom of the camera, the most sensible and intelligent but also more expensive solution as you can see HERE

This tiny battery drains slowly because it keeps the date, time and all settings.
It is charged when the camera is switched on but keeps its charge only if its main-battery (either Li-Ion or 4 x AA's) remains in your Pentax!


Sony is the only manufacturer giving clear instructions concerning this battery:
Does the camera have an internal battery?:
The camera has an internal rechargeable battery for maintaining the date, time, and other settings. This information remains saved in the camera regardless of whether the main battery pack is installed or not, or whether the power if off or on.

The internal battery is continually recharged when the camera is turned on and in use
(Different to Pentax! This CMOS battery does not drain with the main battery/batteries inside the camera!)

NOTE: The internal battery discharges gradually if the camera is only used for short periods of time.
If the camera is not used at all for approximately 3 months, the internal battery becomes completely discharged.



I have to note here, that in many Pentax manuals the advice is "not to store your Pentax over a long period with the main battery inside".

Now, times have changed and most laptops, smartphones and similar devices have their main Li-Ion battery built in without being able to swap it!

Think about it: If you'd have a modern electric car, do you want to swap its battery every time you go on holidays (without car)?
Or did you ever take the battery out of your navigator?

The reason Pentax still recommends this is from old days when one used standard non-rechargeable batteries which could leak badly when drained. NiCd and NiMh rechargeables normally don't leak!

I would be more careful with no-name or aftermarket Li-Ion batteries, because I have seen those swelling which indicates cheap interior!

So back to this little memory- or back-up- or CMOS-battery:

To replace it is much more complicated than replacing the solenoid (when ABF hit your Pentax).
I wrote a tutorial for the K30/50/500 and K-r:
Tutorial: Change Back-up Battery Pentax K-30, K-50, K-500 - PentaxForums.com
It is not an easy job, because the two feet of the MS414 are soldered directly onto two thin conductive tracks on the PCB (Mainboard), a little bit too intensive soldering and those tracks go lose. Then there is no chance to repair this, only solution to remove the CMOS.

Other Pentax DLSR's such as the K7/5/3 K-S1, K-S2 and K-70 have the CMOS on the backside of the motherboard!
K7/K5 and K3 use the SEIKO MS518 which has almost double the capacity of the MS414GE.

HERE a photo of the K5 motherboard, the C-MOS battery. Similar soldering as with the K30/50 and K-r.

But on the K-S1, K-S2 and K-70 you don't want to solder at all on that tiny cramped mainboard.
I'd think Ricoh might change the complete mainboard if they have it for repair.

The CMOS battery holds it charge quite well over the first years, but like every electrical part and particular those containing Lithium they age and then drain quicker, but if not depleted, they do last quite a long time.
But if once depleted, will they not only try to charge and thus drain the main battery but they cannot "be healed" anymore.
This means every time you swap the main battery you lose date/time and your settings!

If you have complex settings, it is a pain then having to repeat this every time you need to recharge your battery.

What has to be done is to check regularely (every 2 month but also depending on climate, i.e. temperature) the charge of your main battery and
recharge it if you don't use your backup camera often and just store it. So it is with my old K10D. I hardly use it but anymore but I value it. Maybe it is some sentiment but I just don't want to let go of it. So every 2 month I check it and use it a little bit.
(Good news with the K10D and K20D is: Those are the only semi-professionals made by Pentax which use the Japansolenoid and here not using them has no affect on the solenoid, it works like a mechanical precise Suisse watch i.e. perfect!)


If your CMOS is depleted, you can try at last this method, sometimes it works:
a) In the Menu wrench-symbol: Auto Power Off: Off (so it won't switch off)
b) Leave your camera switched ON for several hours (don't worry, it will switch off automatically if the Battery is too low)

Maybe repeat this again.
Often this method will help to charge the CMOS at least to that extend that when you quickly swap batteries, it will hold your settings!

A word about the name CMOS or internal backup-battery or memory-battery:
One person finds it quite difficult that I use the name CMOS:
But I had several reasons to use that name:
For aperture-block-failure we have now ABF.

"CMOS" is wonderful short but "internal-back-up-battery" bloody long. To type. We can't invent new names like IBUB or BUB etc.
Hardly anybody would understand a word.
Each time to type those long words, thank-you but NO.

And nobody hitherto had complained when I used CMOS, everybody knew what was meant.
In some non-English-forums the name CMOS is used as well and it makes perfect sense.

Of course most Pentax bodies use a CMOS-sensor but mixing those two would be about the same as mistaking a "dogs bark" with the "bark" of a tree or one's own arm with a gun

So I use CMOS with great confidence here because I find it useful, sensible and logical.

Anybody having difficulties with it:
For god's sake: Relax or drink some CANA

Last edited by photogem; 07-22-2021 at 10:50 PM.
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06-10-2021, 03:14 AM   #2
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The only thing that really bothers me about the loss of cmos memories is my inability to back up my settings other than laboriously writing them all down in a notebook. I don't try to remember all that stuff, so I have to figure it out from scratch, and re-create all my special custom "drive mode" profile settings.
06-10-2021, 11:09 AM   #3
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Anyone try replacing the battery by popping those two spot welds loose and putting a new cell in? There are small spot welders on the market which would allow you to re-spot weld the new cell if that's necessary (might need to dial down the power for this size cell). This would get around doing any soldering work unless that's necessary just to get to the battery.

Mini Spot Welding Machine, 9 Gears Adjustable Portable DIY Spot Welder with Quick Release Pen 18650 Battery Plate Spot Welding, Mini Spot Weld Machine with Nickel Sheet and Charging Cable - - amazon.com?tag=pentaxforums-20&
06-10-2021, 01:00 PM   #4
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Good information to know.

I have no problem leaving my battery in my ks-2 but the k100d only used aa which leaked, died, and the battery drained anyway. It was a pain cleaning out the compartment. Leaving the camera on to recharge then removing is the better option in this case I would think.

Also if you want to leave your camera on to recharge your battery be sure to change your auto power off setting in the menu. The ks-2 can be set for 1-30 minutes or turned off completely.

06-10-2021, 01:52 PM   #5
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QuoteOriginally posted by swanlefitte Quote
Also if you want to leave your camera on to recharge your battery be sure to change your auto power off setting in the menu. The ks-2 can be set for 1-30 minutes or turned off completely.
That's why I wrote:
QuoteOriginally posted by photogem Quote
.... a) In the Menu wrench-symbol: Auto Power Off: Off (so it won't switch off)....
06-10-2021, 03:40 PM   #6
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I believe the batteries come with the surface mount bracket already attached. You have to check the Seiko spec sheet or one of the re-sellers like Digikey. The link to the spec sheets has been posted before. Search the forum for the battery number or it may be in one of the posts/threads linked in the article above.

You would have to un-weld both the old battery and the new one and than re-weld the new battery in place. The risks of damaging the new battery either through heat or compromising the casing are greatly increased.
06-10-2021, 10:28 PM   #7
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There are different types, I have some MS414's here.

It is the MS414GE:
MS414GE | Seiko Instruments Inc. Micro Energy Division
This is different to the Seiko ML414H which Pentax used in the K-m (2000) and possibly K-x:
ML414H | Seiko Instruments Inc. Micro Energy Division
with a mounting bracket spotweldet onto the battery.
That bracket you cannot take off, I tried it and destroyed the battery (it was depleted anyway)
The big problem with this bracket is that it isn't just soldered like the MS414GE onto those two conductive tracks of the printed circuit board but solderen with that wide large minus-section. So you first have to touch the triangular plus part with the tip of your soldering-iron and try to lift it or bend it upwards and then with a larger soldering tip apply heat to that large minus part. I am quite experienced in soldering and have now the cream of the crop Weller which regulates heat very quickly.
And yet the contuctive minus part on the PCP got lose. It just wasn't made for service.

Luckily the MS414GE on the K-r, K30 and K50 it is easier to unsolder. And yet those thin conductive tracks there are very sensitive, once they come off, that's it.
No chance to solder a new battery on them. Then you have to improvise: Glue the battery on the PCP and scratch the laquer off where the tracks are still alright, solder a tiny wire there and its other end onto the battery.

06-11-2021, 12:52 PM   #8
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I wouldn't use solder. You could also use special electric conductive glue

Electrically conductive adhesive (Shieldokit)

Last edited by Sakura; 06-11-2021 at 01:15 PM.
07-19-2021, 07:16 AM   #9
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QuoteOriginally posted by Sakura Quote
I wouldn't use solder. You could also use special electric conductive glue

Electrically conductive adhesive (Shieldokit)
You anyway have to unsolder. With some Pentax bodies that is when more heat is dissipated.
Once unsoldered and no damage to the PCB-board, soldering with low-temperature solder is uncritical.

From what I know from High-End-Audio: A good soldering point was always the best.
07-22-2021, 10:52 PM   #10
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I have found something interesting concering the CMOS battery (and included it as well in the main article together with some word about the name CMOS)

Sony is the only manufacturer giving clear instructions concerning this battery:
Does the camera have an internal battery?:
The camera has an internal rechargeable battery for maintaining the date, time, and other settings. This information remains saved in the camera regardless of whether the main battery pack is installed or not, or whether the power if off or on.

The internal battery is continually recharged when the camera is turned on and in use*


*different to Pentax! There the CMOS battery does not drain with the main battery/batteries inside the camera even if switched off.
I have verified this over a longer period of time.
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