UPDATE: There are some other threads discussing batteries and battery capacities; FYI:
https://www.pentaxforums.com/forums/22-pentax-camera-field-accessories/42336...batteries.html https://www.pentaxforums.com/forums/210-pentax-k-3-iii/427215-battery-question.html https://www.pentaxforums.com/forums/6-pentax-dslr-discussion/422347-wasabi-b...rebuild-2.html https://www.pentaxforums.com/forums/22-pentax-camera-field-accessories/34794...batteries.html
In particular
photogem has been inspecting 3rd party batteries and comparing to original pentax batteries. He has observed:
- a lot of lower quality generic cells in the 3rd party batteries.
- the 3rd party batteries don't have a thermal sensor.
- or a balance charging BMS.
His review of a
Wasabi battery is here. A significant risk with the 3rd party batteries is swelling. A significant advantage of rebuilding is maintaining quality.
Also PF member eccs19 (Mark Evers) has made this YouTube video:
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.
- 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
- 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.
- 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.
- 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.
- These are the connectors. I used a dremel to remove them without bending/twisting. PIC 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.
- 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: lightly sandpaper the surfaces, good quality flux, "hoof" profile soldering iron tip, Pb/Sn flux cored solder seems to work best. 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 . - 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.
- 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.
- 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.