Sonicare Battery Replacement Part 2

Sonicare After my previous blog entry and photos on Sonicare Battery Replacement, I got an email from Ed Elliott, who detailed his own more successful attempt at replacing the batteries in his Sonicare 4100:

Thanks for sharing the info on the Sonicare. Based upon your photos I was able to take some measurements so that I could take a different approach. Rather than splitting the case in half along the original seams, I removed just enough of the case so the batteries could be removed and opened a small area so that I could unsolder the battery connections from the PCB. Your unit is probably beyond hope, but you might want to share the following info on your site.

The cuts


The battery pack

da64b49f9f86eb4c111ec6478c3a1bb3 It works! Powers up. Runs for the full two minute cycle. I haven’t decided how to close it back up. Epoxy? Silicone caulk + heat shrink tubing (may not fit in charger base)? If it lasts until the new Nicads die, I’m doubt if I’ll replace the Nicads again so making the process reversible is not a concern. Prior to this success, I tried this process with an even older model (it even had a different model PCB). Failure. I used the same custom-made battery pack that was subsequently used successfully in the newer Sonicare. I also tested the older one unsuccessfully using 2.4V feed from a bench power supply. I believe the problem was elsewhere on the PCB - the unit had sat in an RV unused for over 4 years through heat/cold cycles and it had been used for several years before that abuse. Given that my cutting approach did not give full access to the PCB plus the fact that I already have the re-batteried Sonicare and a new Sonicare 9500, I decided it wasn’t worth the effort to track down the problem with no schematic.

View the Sonicare photos

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12 Responses to “Sonicare Battery Replacement Part 2”

  1. Ben Says:

    Just a tip - if the sonicare has a fast charge and if Nicads came out of it then Nicads will generally have to go back in, charging circuitry is different between nicads and NiMh - you said you had some 1800mah batteries - these will be nimh - cant get nicad this high. However if the sonicare is a slow charge (15 hours) then it wont matter, will just take longer to get a full charge ( but charge will last much longer)

  2. Matt Says:

    I actually did this with mine over the weekend with great success. It would die every second or third day, needing a recharge. I left it charging all night with the new duracell rechargables and the light was a solid green in the morning and it works perfectly! I wrapped mine in electrical tape just to waterproof it until I come up with something to seal the “battery door” closed. My wife was skeptical at first, but she’s also sick of having hers die all the time, so I may get to do another one this week. Thanks for the great info…

  3. Fred Says:

    The cutout dimensions for the battery compartment were perfect - thanks. My horizontal cuts were about 1/8 inch above the seam and parallel to it. One doesn’t have to cut the slot to access the solder connections on the on/off button side of the handle - when removing the old batteries use a long nose pliers to gently roll the wire back from the spot weld on the batteries and the replacement batteries can be directly soldered to those remaining wires.
    Sincerely Appreciate Your Time and Effort - Thanks, Fred

  4. Steve Says:

    I cracked mine open along the seams using a flexible putty knife (screw driver to start). Desoldered the circuit board (8 spots - used a combination of solder sucker and copper braid). Cut the old batteries out with a knife attachment on a soldering gun. Replaced the batteries with standard AA NiCd. Tested fine. Sealed the body with 3M’s 5200 marine adhesive/sealant. Then realized the same model is on sale for $35 … but this experience was priceless. Thanks for the info! Steve

  5. Pete Says:

    You guys rock — I love the fact that there are others out there like me who will opt to change the battery instead of waste money on a new one and who are also willing to share their knowledge on the ‘net.


    Love it!!!!!!

  6. Justine Says:

    I called the Sonicare Co. today before I read this blog. The service lady told me to place the handle in the charger, hold the green button down for 10 seconds. If it makes a buzzing noise (it did) then the battery has been “reset”. She said to leave it in the charger for 24 hours and it should be like a new battery. Prior to telling me this, I asked if that means I had to spend another $100. on a new Sonicare. She said she was sorry, but yes. I expressed my anger with the Philips company for this, and said I would look elsewhere for another brand. (Oral B)
    That’s when she told me about the reset. It hasn’t been 24 hours on the charge, so I don’t know if it actually works.

  7. Matthew Says:

    Thanks for the extra tips, everyone!

  8. crash Says:

    I followed this guide and the cuts were excellent! i don’t know what model sonicare i have, but it was given to me sometime in 2001. it starting cutting out early on the 2 min intervals even on the first charge in january of 09. i didn’t try that 10 second hold down though.

    I bought two NiH 2000mAH AAs (it says 1.2V on them) from Batteries Plus ($8) and they’re in there now, works so far! i haven’t tried a recharge but the light comes on when i stick it in the charger.

    I only used a regular soldering iron for my work. i had some trouble with the PCB solder holes because i couldn’t get the solder out of them. i eventually forced one end of a paper clip through the hole while heating up the other side of the solder hole with the soldering iron. that provided a hole big enough for my njew wires to get in.


  9. Kaicanoe Says:

    I love how the sonicare works, but their batteries just don’t last long. The reset in the charger worked ok, but I could only get about a 2 years out of the unit. I had purchased xtra heads so I wanted to keep the unit.
    Well, Costco came up with $20 off a $99 package (2 handles 4 brushes 1 charger 2 travel paks) so I opted for it.
    In the package is a registration card for a $29.99 gift certificate. Now we are cooking. Said I could register on line & it would be sent to me. I did that & got a WELCOME email. I did a CHAT online with them & they told me I had to fill out another form, mail it in, then they would send me the certificate.
    This is totally out of context as to what I just read. Now I am waiting for their manager to contact me & convince me that the switch & bait technique is ok. After all, this is the US, right? All screwed up too.
    Seems to be no integrity, no reliability by sonicare.
    I did take apart my old unit, but for the $79 I paid for 2, works out to a very reasonable $39.50 for one, including a pair of extra brushes..thanks to Costco.
    I still use my old Braun which has outlasted 2 of sonicares. I use it in the a.m., & the sonicare at night. Now I have 2 so it should last twice as long, eh? hehe.

  10. Ed McCullough Says:

    I replaced the AA batteries with two NiMH batteries. I cut an opening on the back (the side that does not have the green button). The opening for access to the batteries should be cut starting 2.2 centimeters from the base. The other side of the opening for access to batteries is 7.5 centimeters from the base. By “base” I mean the end of the toothbrush that rests on a tabletop when the toothbrush is set upright on a table. Cut all the way through the plastic shell from the seam line on one side to the seam line on the other side. Then you need to cut along the seam lines. Y ou will be able to loosen and remove enough of one of the covers to have good access to the batteries. Be sure to mark the + and - leads to the batteries, so that your replacement batteries are put in with the proper polarization. I chiseled off the wire leads that were soldered to the batteries. There was too little room for me to solder the leads to the batteries, so I jammed wooden wedges into the apparatus to hold the leads against the batteries. Next I put back the piece of cover that I had cut off and glued it in place with the glue E-6000. Silicone cement or bathroom caulking cement should work as well. My toothbrush is working well again. I hope my instructions have been good enough for you to follow.

  11. Pete Says:

    I now have 2 handles with dead batteries . I also have several now replacement heads. When they died , I puchase a n inexpesive Crest Sonic model (replaceable AA batteries and heads) and my dentist told me my gums are fine . I guess that I will replace the batteries in one Sonicare handle to use up my stock of heads but I am done with them aften that .

  12. Gss Says:

    I think if you put your toothbrush on the charger every time after you use it, you’ll wear out the batteries quicker. I usually use mine until it’s completely discharged before putting it back on the charger. Mine is still going strong after 3 years.