22nd November
written by Todd Harrison

In this video episode I show how to replace solder tab rechargeable batteries in some very useful consumer products that would otherwise end up in a landfill. I use more common and cheaper none solder tab reachable batteries and show how to safely and effectively solder on the tabs.

First up was the solder tab type AA 1.2v Ni-Cd in my beard trimmer. I know, not the most attractive thing a man wants to see in his bathroom.

Then my programmable Christmas tree light timer which needed a coin cell 1.2v Ni-MH with PCB mounting tabs.


I noted in the video that it was interesting they were powering the timer controller using a bridge rectified AC to DC converter.  I was surprised to see this without the use of a step down transformer before the rectifier circuit.  Further research, I found this is quite common in consumer products that require less than 70mA and it can be done safely and cost effectively.  There are some pros and cons to this approach. If you want the full details with the math and picking the correct sized passive devices  you can review this nice article at Microship.com.  For the power conditioning circuit which is closes to what is in my timer see Fig.12 in the article.




  1. robert

    Good thing you got it fixed!

    Why did you assume it would have ended up in a land-fill? To me it seems the plastic parts would recycle quite easily.

  2. […] have gone south. They’re not meant to be consumer-replaceable, but that did stop him from cracking them open and swapping out the solder-tab batteries […]

  3. big J

    good tutorial, however i find if you sand or file the contacts a little more you find a brass coloured base that is much easier to solder to. also tinning the areas to be soldered is better for me. good work though!!
    all the best.

  4. bylo

    Great job! As it happens I had the identical Philips beard trimmer as yours. After the first battery died I used exactly the same techniques you show to replace it. The only difference was that I used a NiMH AA rather than NiCD. Both are 1.2V. The NiMH had about twice the mAh rated capacity and ran the trimmer at least twice as long as the original battery. After about 5 years that battery died so I did a second battery replacement and got another few years out of the trimmer. I finally had to scrap the trimmer when the bearings in the motor seized—probably because I didn’t oil them as often as I should have. Oh, well.

    BTW the replacement trimmer, also a Philips, is put together with glue rather than a screw, so when its battery dies I don’t know how I’m going to open it to do the replacement.

  5. 28/11/2011

    @ byro Nice work! I keep the battery technology the same unless I’m totally changing the power and charging system. I think my trimmer will last a long time being I use it about 3 time a month at most.

  6. Brad H.

    Nice tutorial. I really appreciate it. I have that exact same timer. The battery hasn’t died yet, but I am sure it won’t be long. Thank you and keep up the great posts! I love keeping things out of the landfill too!

  7. 02/06/2012

    Why not use a capacitor in series, which is what they were doing on the timer (that big red cap was surely in series with the mains live) … I know there are reactive issues but at such small loads does it matter? — Your circuit is basically how almost all hair dryers work, this is how the fan is powered by a tapped heating element.


  8. […] Replacing solder tab rechargeable batteries […]

  9. LMP

    I had a similar problem, but my Phillips trimmer did not have screws.

    The trimmer body appeared to be glued, but I managed to pry it open and replace the battery.

    The two halves of the body were secured by tabs that were clearly designed to break if opened, so afterwards I had to use tape to keep the body closed.

    BTW, I did not bother soldering the new battery. I used insulating tape to keep the terminals in place, and it worked like a charm.

  10. 22/11/2012

    @LMP, That is a good idea. I’m glad it worked, to bad most consumer products are not serviceable when the only thing wrong is an old battery.

  11. 28/11/2012

    Hi Todd,
    Great post. I am having trouble opening my Phillips trimmer. It ain’t working at all so I suspect that the batteries have worn out or maybe the motor is dead. Can’t say anything till I open the darn thing. 😛

    Anirudh Bahadur

  12. 28/11/2012

    @Anirudh, Thanks. Let me know if you get it working.

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