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Thread: DIY PX28 or 4SR44 Battery

  1. #1

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    DIY PX28 or 4SR44 Battery

    The PX28 battery (same as 4SR44 or 4LR44) is a 6V battery that is used in some medium format cameras and light meters. I know it's used in the Pentax 6x7, some Bronicas, and the Mamiya RZ67. This battery is actually made up of four LR44 batteries (or SR44, G13 etc). The LR44 batteries are ubiquitous, and you can usually get several for a dollar. Unfortunately, the PX28 battery seems to be quite expensive, and not so easy to find. You can try to stack four LR44 batteries in the space for a PX28, but the overall length will be too short unless you add a spacer of some kind (like a folded up piece of tinfoil).

    This DIY is to make your own PX28 battery using the bits from an old dead one.

    1) Take an old dead PX28 battery and with a pair of small pliers pry the outer metal casing away from the body at the seam at one end.

    2) Work you way down the seam to further pry the outer metal casing away from the body. This will expose the inner plastic or paper tube that holds the four LR44 batteries.

    3) Once the outer metal casing is removed, the smaller LR44 batteries can be pushed out of the inner tube along with the metal end contacts. You'll want to keep the tube and the metal end contacts for the new battery.

    4) There's some variation of the inner sleeve style between various manufacturers. The Varta ones I've tried have a plastic sleeve that's capped at one end with a smaller hole. This is nice, since it keeps the positive contact from falling out the other end. The Maxell has a thin cardboard tube, and a Duracell just has a piece of paper that's rolled up as a tube but isn't joined. If it's just an open tube, then you need some tape to hold the batteries from popping out the ends. Put the four LR44 batteries in the tube in series (each in the same orientation). The positive metal end contact will have a taller protrusion. and this should be placed in contact with the positive battery contact at one end. The metal contact for the negative end will have a shorter protrusion. I don't put that one at the outer end, since it's too easy for it to fall off. I put that one in the middle of the battery stack, with the protrusion in contact with a negative end of battery. This leaves the outer end battery with it's own negative end exposed.

    5) Wrap some thin white freezer tape around the sleeve such that the tape extends a little over the end of the sleeve. This is so you can fold the tape over the end of the sleeve to prevent the LR44 batteries from falling out easily. The freezer tape is nice since you can write on it to identify what type of battery it is.

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  2. #2

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    Re: DIY PX28 or 4SR44 Battery

    The Varta battery was really nice. The metal positive contact can fit right over any LR44 battery, and the cap at one end of the plastic sleeve keeps everything contained at one end.

    I should also add that some of the LR44 batteries I removed from the PX28 were still perfectly fine. It seems like the dead ones are really dead, and the good ones are really good. Maybe it's just a fluke.
    Attached Thumbnails Attached Thumbnails PX28-Battery-5a.jpg   PX28-Battery-6a.jpg   PX28-Battery-7a.jpg  

  3. #3

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    Re: DIY PX28 or 4SR44 Battery

    The 6 volt PX28 or 4LR44 alkaline battery is not common in stores as far as I know, but it is easy to find on US ebay for ~$1-2 a piece (I don't know about Canadian ebay). The 4SR44, silver oxide version, may be more expensive. It seems that their primary use now is in electric collars for dogs - maybe it would be findable in a pet store. Not to diminish your ingenuity. I used to worry about finding these batteries, but now I get several and keep the extras in the fridge.

  4. #4

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    Re: DIY PX28 or 4SR44 Battery

    I didn't know they were used for dog collars. Maybe they're more readily available than I thought.

    Still though, it always seems to be the case that when you need it urgently, you can't find one, or the one you have is dead. The nearest dollar store will always have LR44 batteries, plus, I like to tinker.

  5. #5
    Eric Woodbury
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    Re: DIY PX28 or 4SR44 Battery

    Amazon, 10 ea for $6. Ebay certainly has them. Use alkaline version.

  6. #6

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    Re: DIY PX28 or 4SR44 Battery

    One big downside with stacking button batteries is the multi contact surfaces don't always make perfect contact, and cause partial or full intermittent issues, resulting in device making erratic operational issues... Cameras and meters using stacked batteries have given me problems at times, usually if was cold and/or damp...

    But the 6v cells off the shelf have also caused issues, as some sat on shelves a long time (I suspect) have not provided a short or any life in some cases, but have had better luck with the (expensive) lithium types...

    Biggest problems were with a borrowed RZ-67 (which battery indicator would light, but go 1/400th second manual default speed), a Minolta Flash meter III (the display would ghost on and off), and countless Canon AE-1 35mm cameras others would bring me that jammed after battery died prematurely and they tried to wind them)...

    Not the most trusty battery... :-(

    Steve K

  7. #7

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    Re: DIY PX28 or 4SR44 Battery

    Quote Originally Posted by LabRat View Post
    One big downside with stacking button batteries is the multi contact surfaces don't always make perfect contact, and cause partial or full intermittent issues, resulting in device making erratic operational issues... Cameras and meters using stacked batteries have given me problems at times, usually if was cold and/or damp...

    But the 6v cells off the shelf have also caused issues, as some sat on shelves a long time (I suspect) have not provided a short or any life in some cases, but have had better luck with the (expensive) lithium types...

    Biggest problems were with a borrowed RZ-67 (which battery indicator would light, but go 1/400th second manual default speed), a Minolta Flash meter III (the display would ghost on and off), and countless Canon AE-1 35mm cameras others would bring me that jammed after battery died prematurely and they tried to wind them)...

    Not the most trusty battery... :-(

    Steve K
    I hadn't thought of that, but I can certainly see how that could be a problem. Another issue is the leaking of these types of alkaline batteries. I'm sure we've all been burned by this. I always take the batteries out after I've finished using the device, but it is a pain in the arse.

    It got me thinking about a lithium alternative. I know they have 3V lithium batteries that replace 2 LR44 batteries, and I've used them in a few 35mm cameras. The nice thing about the lithium batteries is that they don't leak, and they have a long shelf life, but they are more expensive. The 2 LR44 replacement is a lithium CR11108. After some searching I found that there is a lithium PX28 replacement that is a 2CR11108. This is a 6V battery that I assume is two 3V lithium batteries in series. This reduces the number of internal contact surfaces from 3 to 1, so it's a significant improvement.

    I think it would be worth it to spend the extra money for a lithium version now that I know it exists.

  8. #8
    Eric Woodbury
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    Re: DIY PX28 or 4SR44 Battery

    If the device uses burst of hi current for a motor, then use lithium. Meters and such use very little current. When I was designing and selling light meters, always recommended alkaline. Lithium is a waste for a light meter. Never had one leak in a meter, yet. Just change them every year and no surprises.

  9. #9

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    Re: DIY PX28 or 4SR44 Battery

    Quote Originally Posted by sharktooth View Post
    The PX28 battery (same as 4SR44 or 4LR44) is a 6V battery that is used in some medium format cameras and light meters...
    Quote Originally Posted by Eric Woodbury View Post
    ...Meters and such use very little current. When I was designing and selling light meters, always recommended alkaline. Lithium is a waste for a light meter. Never had one leak in a meter, yet. Just change them every year and no surprises.
    I assume Eric incorporated voltage regulation in his meters. Pentax didn't when designing its Digital Spotmeter. For that one, use only silver:


  10. #10

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    Re: DIY PX28 or 4SR44 Battery

    After some further investigations this morning, I found out that the Varta and Maxell batteries shown in the photos were silver oxide based. I also took apart a Duracell battery that was alkaline based.

    I have two old Varta batteries that were still working, and after checking those ones I discovered that they are lithium versions V28PXL. The L at the end signifies lithium, and they were indicated as "lithium" on the label, but in very small print. I don't know why they wouldn't promote the fact that they were lithium batteries. In any case, I still had the packaging for one of them, and the best before date was Dec 2010. Not bad for a 10 year out of date battery with no special storage.

    I checked one of our big photo retailers here in Canada, and they sell the Varta V28PXL batteries for $20 each. That's why I remember those things being so expensive. Duracell makes a lithium equivalent in their 28L version, and Eveready's lithium version is L544. All of these are expensive.


    I wouldn't leave any alkaline battery in any device I cared about, especially old film cameras. Alkaline batteries will leak in the packaging, so low current devices are no guarantee of protection. Now that I know there are lithium versions available, I need to reconsider the cost/benefit analysis.


    I'll probably buy a couple of the lithium versions to use in medium format cameras, since it's a relatively small price to pay for no-leak security. The lithiums also last a really long time. I'll use my homemade alkaline versions for camera testing.

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