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Rebuilding a pentax D-Li90 battery
Posted By: marcusBMG, 03-20-2020, 02:12 PM

PS I'll take your old/dead batteries for rebuilding - PM me.


As Li Ion batteries age the charge capacity steadily diminishes. As you can see in the first pic, the test result for one of my D-Li90's is now only 985mAh*, ~ half the original spec capacity of 1860mAh. It is a pretty old battery, the date code is 201009 ie this is over 10 years old so it's done pretty well.
While both pentax and third party batteries are readily available, the pentax battery is overpriced and you don't really know what the quality is of the third party ones. My own experience of buying and checking Li Ion battery cells is that outside of the main brand names like panasonic, samsung etc it's a bit of a lottery, the market is riddled with low quality or dodgy cells (especially ebay - for examples of really dodgy cells check out
- anything advertised with an OTT capacity rating ie above ~3500mAh can be assumed to be dodgy).

So the advantages of rebuilding are 1. cost and 2. quality control.


WARNING. This is what I did. You engage in something like this at your own risk. It is up to you to have sufficient diy and electrical know how. Don't disassemble a battery that hasn't been discharged. Take proper health and safety precautions.
TOOLS: modelling knife, soldering iron, plastic glue, gluegun. Multimeter useful for testing. Spot welder ideal for reassembly.
  1. The two halves of the case are glued/sealed together. I worked the tip of a knife blade along the join to separate. PIC 1
  2. The battery is a straightforward 2S/1P, 18500 cells (ie 18mm dia, 50mm length). There is a balance charging connection BC and a small control board CB. The MH12210 ID'ed these cells as panasonic. PIC 2.
  3. The cells are stuck to the base, ease out carefully. Note the polarity arrangement. I have already pulled off the spot welded link strip on the R ends. PIC 3.
  4. The control board is going to have to be soldered off to access the cell ends. PIC 4. The end solder points S are the ones. I intend to use the same connectors and (later) used some desolder wick to (partially) clear the connection points. PIC 5.
  5. These are the connectors. I used a dremel to remove them without bending/twisting. PIC 6.
  6. It is a good idea to use identical new cells. As well as varying capacity and quality, different cells are designed for different purposes eg high current for drills and tools. I think these are more oriented to capacity and durability. Panasonic MH12210 replacement cells are available from a number of suppliers, typical cost seems to be ~6 each (UK). The supplier I enquired with (ecoluxshopdirect.co.uk) were out of stock but advised that the slightly cheaper Amsplus cells were essentially identical quality and spec so I went with that.
  7. A gluegun is standard for joining cells into a block PIC 7. The tags can be soldered back on but I have the right tool for this job, my newly commissioned MOT spot welder PIC 8.
    If you are soldering, it is a bit more risky, in fact the seller of the cells I bought remarked that he had had a customer who had had problems soldering cells for a camera battery. My own tips: good flux, "hoof" profile soldering iron tip. Also there is little room in the case for "lumpy" soldering, you will need to try to make the joint as flat as possible.
    The rear tags are straightforward, then the front tags and control board are the ticklish part. I used bluetac (less secure, easier to microadjust position)/double sided sticky tape (more secure) to carefully position and hold the tags PIC 9 .
  8. Then resoldering the control board went smoothly, just a second or two contact with the iron and the old solder melted and the tag came though the slot.
  9. I now had a disconcerting moment when I couldn't get a voltage reading out of the battery. But the battery started charging fine (case left open to observe, check temperature by touch PIC 9) so it was just the control board registering that the cells were low and doing its job, switching the battery off.
  10. I suggest either a cyanoacrilate superglue, or plastic-weld solvent (I used the latter) to rejoin the case. Done (pic 10), battery works perfectly.
Overall I can say this is a straighforward, easy in fact, little diy exercise.


*except that later I realised that the Imax was faulty, consistently under-rating all the cells I tested with the discharge capacity function! The true capacity of the DLi90 was probably around 1500mAh - still significantly down on its rated 1800mAh.


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Last edited by marcusBMG; 03-23-2020 at 06:35 AM.
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03-21-2020, 12:23 AM - 1 Like   #2
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It is wonderful. But how much does a spot welder cost?
03-21-2020, 06:41 AM - 1 Like   #3
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QuoteOriginally posted by Ivan Quote
how much does a spot welder cost?
Well my diy build cost under 25, comprised mainly of 10 for the control board, 7 for 2m of welding cable and 4 for a small 9v ac transformer. The MOT was from a junked microwave so was free, as were the other bits I cannabilised like the metal panelling, feet, handle. It's a good project actually, google microwave oven transformer spot welder.
03-22-2020, 01:44 AM   #4
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I am very interested in this project. It's really useful. I have no idea how to build one like this. Can I count on your help?

03-22-2020, 02:29 AM   #5
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I will say that I am amazed by the DIY capabilities of our members.

(Still planning to purchase new batteries when my old ones wear out).
03-22-2020, 07:15 AM - 1 Like   #6
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QuoteOriginally posted by Ivan Quote
Can I count on your help?
(i assume you mean a spot welder) I'd be happy to advise as best I can. Check out:

Voltlog #207. uses 3rd party controller board like I did. U tube video nUR-giwn4z0

table top machine shop. Building a Spot Welder from a Microwave Transformer.. Uses marine battery lead, custom programed time controller. Video 2 discusses using a vario resistor to protect the SS relay. Videos: dRTplGUzw28 ; PW-RbgmcPHo

Alexander Hartdegen. Circuit diagram, use of dimmer to control power, subbers, V-A meter. Vid #2 - build. Videos: MUId45iUr08 ; McKbU9Bu 30

Nematic. DIY 18650 battery Spot Welder! | Microwave Transformer. Uses relays and capacitors to control the time. Custom pcb. Video: W3c242TUsvs

Creative Channel. How To Make Mini Spot Welder Using old Microwave Transformer. ATX psu box. Timer control using off the shelf unit. Video: PuKu5J- 64

Donny Terek. DIY Spot Welder From Microwave Transformer | HOW TO. Controller board, foot pedal, nice box. video: UseccvORpk8

There are other ways to achieve spot welding too. Before I latched on to the MOT build I was looking at using a car battery (see U-tuber darkkevind ) but was confounded when I tried to find the bits from breakers yards, other modes use Li Ion batteries or capacitors.

Last edited by marcusBMG; 03-27-2020 at 11:10 AM.
03-22-2020, 12:45 PM   #7
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Thank you, that's what I needed.
03-26-2020, 07:04 AM   #8
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QuoteOriginally posted by marcusBMG Quote
PS I'll take your old/dead batteries for rebuilding - PM me.


As Li Ion batteries age the charge capacity steadily diminishes. As you can see in the first pic, the test result for one of my D-Li90's is now only 985mAh*, ~ half the original spec capacity of 1860mAh. It is a pretty old battery, the date code is 201009 ie this is over 10 years old so it's done pretty well.
While both pentax and third party batteries are readily available, the pentax battery is overpriced and you don't really know what the quality is of the third party ones. My own experience of buying and checking Li Ion battery cells is that outside of the main brand names like panasonic, samsung etc it's a bit of a lottery, the market is riddled with low quality or dodgy cells (especially ebay - for examples of really dodgy cells check out this video - anything advertised with an OTT capacity rating ie above ~3500mAh can be assumed to be dodgy).

So the advantages of rebuilding are 1. cost and 2. quality control.


WARNING. This is what I did. You engage in something like this at your own risk. It is up to you to have sufficient diy and electrical know how. Don't disassemble a battery that hasn't been discharged. Take proper health and safety precautions.
TOOLS: modelling knife, soldering iron, plastic glue, gluegun. Multimeter useful for testing. Spot welder ideal for reassembly.
  1. The two halves of the case are glued/sealed together. I worked the tip of a knife blade along the join to separate. PIC 1
  2. The battery is a straightforward 2S/1P, 18500 cells (ie 18mm dia, 50mm length). There is a balance charging connection BC and a small control board CB. The MH12210 ID'ed these cells as panasonic. PIC 2.
  3. The cells are stuck to the base, ease out carefully. Note the polarity arrangement. I have already pulled off the spot welded link strip on the R ends. PIC 3.
  4. The control board is going to have to be soldered off to access the cell ends. PIC 4. The end solder points S are the ones. I intend to use the same connectors and (later) used some desolder wick to (partially) clear the connection points. PIC 5.
  5. These are the connectors. I used a dremel to remove them without bending/twisting. PIC 6.
  6. It is a good idea to use identical new cells. As well as varying capacity and quality, different cells are designed for different purposes eg high current for drills and tools. I think these are more oriented to capacity and durability. Panasonic MH12210 replacement cells are available from a number of suppliers, typical cost seems to be ~6 each (UK). The supplier I enquired with (ecoluxshopdirect.co.uk) were out of stock but advised that the slightly cheaper Amsplus cells were essentially identical quality and spec so I went with that.
  7. A gluegun is standard for joining cells into a block PIC 7. The tags can be soldered back on but I have the right tool for this job, my newly commissioned MOT spot welder PIC 8.
    If you are soldering, it is a bit more risky, in fact the seller of the cells I bought remarked that he had had a customer who had had problems soldering cells for a camera battery. My own tips: good flux, "hoof" profile soldering iron tip. Also there is little room in the case for "lumpy" soldering, you will need to try to make the joint as flat as possible.
    The rear tags are straightforward, then the front tags and control board are the ticklish part. I used bluetac (less secure, easier to microadjust position)/double sided sticky tape (more secure) to carefully position and hold the tags PIC 9 .
  8. Then resoldering the control board went smoothly, just a second or two contact with the iron and the old solder melted and the tag came though the slot.
  9. I now had a disconcerting moment when I couldn't get a voltage reading out of the battery. But the battery started charging fine (case left open to observe, check temperature by touch PIC 9) so it was just the control board registering that the cells were low and doing its job, switching the battery off.
  10. I suggest either a cyanoacrilate superglue, or plastic-weld solvent (I used the latter) to rejoin the case. Done (pic 10), battery works perfectly.
Overall I can say this is a straighforward, easy in fact, little diy exercise.


*except that later I realised that the Imax was faulty, consistently under-rating all the cells I tested with the discharge capacity function! The true capacity of the DLi90 was probably around 1500mAh - still significantly down on its rated 1800mAh.
Excellent post with tons of useful info.
Thanks for sharing,
barondla

03-27-2020, 10:52 AM   #9
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Great post - was waiting for my first battery to play out so I could find out what is inside - you answered my question and provided a lot more. Cudos!
04-07-2020, 08:27 AM - 1 Like   #10
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The less than great thing about using third party batteries, or rebuilding a D-LI90 with some spare part is that the max voltage of those Li-Ion batteries is not the same as the max charge voltage of the OEM Li-Ion. Optimized full charge of batteries require precise charge up to the max voltage without exceeding that voltage. That's why charging non-OEM batteries with a Pentax charger either result in less battery capacity (when battery actual max voltage is higher than charger stop point) or less battery life time (when battery max voltage is lower than charger stop point). Best is to buy original Pentax batteries even if more expensive, are a lot less expensive than cameras and lenses, rather than trying to save a few bucks and have less then optimal capacity or life time.
04-07-2020, 10:39 AM - 4 Likes   #11
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Well the usable cell capacity (which is what we're talking about here really, not voltages per se) depends on two things: mainly the designed cell capacity as per specs; secondarily to what voltage it is charged to. 4.2V is totally standard, it is unusual actually to find a cell or charger that charges to a different voltage. In practice different chargers can result in slightly different end voltages. Some enthusiasts online are quite particular about what is a good end voltage, specifically many suggest it is better to go a bit less than 4.2v eg 4.1v to improve longevity and frown on chargers that tend to go over 4.2v slightly.
In any case as I point out in my write up the original pentax battery uses a 3rd party cell from panasonic. If you use the same replacement cell, new, that should avoid any issue you mention.

The usage life of my rebuilt battery is excellent btw, like a new one, I can once again grab the camera and assume I have life in the battery and usually be right.

Last edited by marcusBMG; 09-09-2020 at 07:19 AM. Reason: more info
08-10-2020, 10:58 AM   #12
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I know this post is a few months old, but I'm just seeing it.Thanks for the interesting look at a battery rebuild, and for introducing me to DiodeGoneWild on YouTube. I see hours of my life wasted watching those videos!
09-09-2020, 07:07 AM   #13
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DIY sony NP-F type battery for LED array

This is my latest project. The LED array is designed to take a couple of different Li Ion camcorder type (sony NP-F) batterys, or 6 AA's. I didn't fancy burning through lots of AA's, moreover finding 6 similar ones similarly charged in my box is basically next to impossible. And the Li iOns were a bit pricy. So I acquired a few cheap s/h cells, 2500mAh ($ each) and the little pcb 2S control board. Bit of diy work to contruct the pack with the indented +/- terminals correctly spaced (threaded holes in the polycarbonate, short lengths of brass bolt) but works pretty well. The charging connection is a standard JST, for which I already have a connector with my Imax B6 smart charger. Battery in pics 1, 2 isn't quite finished. A finished battery with shaped plastic end cover and heat shrink sleeve shrinked is fitted into the LED in pic 3.
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Last edited by marcusBMG; 09-09-2020 at 07:24 AM.
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