Rebuild cordless phone battery pack

The battery packs on some older Panasonic cordless phones are nearly dead (thankfully newer units take standard AAA rechargeables), genuine replacements seem pretty expensive, and the cheap replacements (before knowledge of BLF and battery fakes) are quite poor in performance.

  • Is it possible to non-destructively disassemble the battery packs and replace the cells?

* What cells are they? Ni-MH, 1.2V, but they are 48mm (replacement) or 49mm (original Panasonic) long, which is longer than the typical AAA battery at ~44mm. The diameter seems similar to AAA.

I`ve tried twice to take these apart and failed miserably :person_facepalming: “twice” :person_facepalming: , ended up buying a whole new phone set @ costco.

Yeah, it’s really not obvious to me if and how the battery packs come apart. And yes, given the cost of the genuine batteries, it seems unfortunately more cost effective to get new phones… so irritating.

We already have a newer set too, and my favorite part is that they don’t have battery packs. After several years, we changed the AAAs in them once so far. Nice and easy. But as for the older sets, it would be sad to dispose of them when they still work fine in every other way for except battery life.

Huh? They’re not just 3 cells shrinkwrapped together with the little pigtail connector coming out?

No, that’s another type. Are my pics not showing?

Not here, but I’ve had “issues” with certain pix not showing. Not sure where the fault lies.

Weird. I thought Imgur works fine here. Here are the links in case it helps:

i see pics, they are very good and detailed, prbly a browser issue if you can’t see them, but in any case seems like there is no way to open them without breaking something, but breakage can be limited, and not critical to function

As others have said, these are hosted at and the domain might be blocked for you due to some ad-blocking or script-blocking feature or add-on in your browser. Some filter lists seem to include imgur by default.

I’m also having some with certain images not appearing at BLF during the past week as well, even in my own posts, but this is likely some filter in my browser that’s suddenly over-active. I get the imgur images in this thread just fine, though.

I can’t really help with these Panasonic battery packs, but I totally understand your frustration. I’m still using cordless phones as well and have found that the AAA cells are much better than the proprietary packs, but that my Pana phones, which are about a decade old, have terrible charging circuitry and tend to wear out the cells fairly rapidly. My phones seem to have no real charge-cutoff logic; it seems to be just a timer of some kind.

The phone might calculate a charge time based upon how long it’s been in use (i.e. talk time), as the charge time does seem to vary proportionally, but it will always perform a full charge whenever the cells are replaced or handset power is interrupted.

This means that I must fully discharge the AAA’s before inserting them into the phone or they will simply get cooked for hours. Even in everyday usage, I’ve randomly taken the battery cover off the back and found that the cells are often very warm to the touch for no good reason; they are being over-charged.

While I’m glad to have replaceable batteries, I’m rather annoyed that Panasonic cheaped out on the charging circuitry.

  • Amazon Basics set of 8 NiMH 850mAh AAA’s for $10. I bought 2 sets of these because the above set wasn’t available a couple years ago, but the extra 50mAh is probably worthless here, if it even exists (Amazon seems to rate capacity fairly accurately, though).

I’ve seen Panasonic cordless phone sets at the thrift store many times. There are usually several handsets and an answering machine base unit in a bag for $5 or $10.

Rather than fiddling with the old-style battery packs, perhaps it’d be easier to check your local craigslist or Goodwill stores for a gently used set that takes AAA cells. Swap the old cells with IKEA, Eneloop, or Amazon Basics NiMH.

Ah, these I can see…

(HHR-P104, etc.)

And looking up-top, now I see them there, too.

Odd. Maybe a temporary imgur glitch…

Wellp if all you need is the frame and contacts, you can dremel down those 2 crossbeams to get at the cells, then pry ’em out and solder/crimp/whatever the new cells to fit the frame. Hotglue ’em to hold ’em in place.

AguassissiM Do you remember the structure of the packs? At least the “failures” could serve a purpose.

leftdisconnected Hmm that’s too bad about the charging circuitry. I wondered how good it was when I put some LADDAs in the cordless units that take AAAs. Still, both the packs and AAAs lasted somewhere between 5-10 years so I’m guessing that’s about what could be expected of the cells.

goshdogit It is most definitely easiest to get new units, but I find it a shame to get rid of something that works. We actually have three sets now. One set (with answering and two units) that uses AAAs, and two older sets that have the unfortunate battery packs.

Lightbringer Cutting the “crossbeams” was my thought too, and then maybe just taping it all back together. But the other issue is that the cells in the packs are several millimetres longer than a typical AAA. Wondering if there is anything special about them or if it’s just another middle finger to the consumer.

From the outline of the shrink wrap, the cells in the packs look like they have a separate board under the cells, similar to the circuit board of protected Li-Ion cells. Do some Ni-MH cells have extra features? Or, if they’re just dummy spacers maybe I could salvage them… hmm

Thanks for the ad blocker tip. I was having trouble streaming my local news broadcast. I turned off AdBlock and now it works.

get flat top aaa cells and the rebuild gets easier.
the button tops are the clearance problem.
rebuilt lots of those packs over the years.
some have easy to release latches that will reclose after you are done replacing cells.

How so? The button top AAA cells are already 4-5mm shorter than the cells in the packs.

Do you recognize any latch releases in the images posted above?

I finally cut open the battery packs by cutting the “crossbeams”. It doesn’t look like there is a non-destructive way of opening them. For the curious here are some pics:

The batteries are tack-welded in series with metal strips, and their 48mm length is longer than a standard AAA, though the diameters are the same. Seems not impossible, but rather a pain to rebuild with fresh cells.

oh so the rare oddball 4/3 aaa or such.
rebuild with the eneloops and forget the extra space. close to original capacity.
ignore the 900mah rating on the aftermarket.
unlikely to be as good as the original.

Ignore the extra space… that could work, and give room for solder.

I don’t want to mess up beloved Eneloops so I may or may not try rebuilding with other cells.

The “900mah” capacity is definitely not real.