This project shows you how to replace the batteries in an Oral-B Sonic Complete toothbrush. This is a great electric toothbrush, but Oral-B tells you to toss it when the internal rechargeable Ni-CD batteries die. Aside from the wastefulness of that, the toothbrush costs about $90. So, when my father's toothbrush finally died, we decided to replace the batteries anyway. This project requires soldering, and there's some risk you'll destroy your (presumably nearly dead) toothbrush when taking it apart and putting it back together.
Step 1: Supplies
The key here is ordering the battery. We found ours at the NICD Lady, a Sanyo KR-600AE with solder tabs. As of 7-29-2009, you could find it on this page:
As far as I can tell, all NiCD cells are 1.2 volts, and this one appeared to be almost exactly the right size. Since the toothbrush can hold enough charge when new to go for a week without recharging, we figured that even if these didn't exactly match the capacity of the original NICD cells, they ought to work.
Because the device was designed for NICDs, you ought to replace the battery with a NICD.
Beyond that, you need a soldering iron, solder, maybe an X-acto knife, some long-nosed pliers, a hemostat (we used a paperclip instead), and some electricians' stable.
Step 2: Take the End Cap Off the Toothbrush
STOP: You need to know two things before proceeding. First, the innards are spring-loaded. Second, the base of the toothbrush remains connected to the body of the toothbrush with four THIN copper wires. These are fragile. So, you need to keep a tight grip on the toothbrush when you do this step.
The "wrench" for unlocking the base of the toothbrush is on the back of the charger.
Get a good grip on the toothbrush, push it onto this "wrench", and give it a slight twist while pushing it solidly into the charger. It takes little effort and about an eighth-turn to unlock the toothbrush bottom. When you feel it pop, gently remove the toothbrush. If the base of the toothbrush sticks to the charger, get a screwdriver or other small instrument in there and gently pry it loose. Don't try to pull it off via the four thin copper wires.
Step 3: Remove the Innards
The entire insides of the toothbrush will come out at this point. The bottom edge of the internal "works" engages the outside plastic casing. So you may want to reach up with needle-nosed pliers or a small screwdriver and pry the edge of the inside "works" away from the outside casing, as you push the "works" out from the other end.
To be clear -- the entire thing comes out, so push the steel rod where the brush attaches, as you disengage the bottom end of "the works" from the exterior casing. This does not require a lot of force. Once it's free, its just the friction of an O-ring seal at the top that is holding the works in.
Step 4: Remove the Old Batteries
The batteries are soldered in. There are only two rules here: 1) Leave as much of the solder tab attached to the circuit board as you can, and 2) don't break anything. You'll see why you want to leave the solder tabs on the board when you go to put the new batteries in. Beyond that, you're on your own. I used a combination of long-nosed pliers and an X-Acto knife to pop as much of the tab off the battery as possible. Good luck... Trust me, take the time to leave as much of the tab on the board as possible. You will thank yourself as you go to solder the new batteries in.
Step 5: Solder the New Batteries Together,
OK, so I did this exactly once in my life. I am sure I could do better with practice, but here are the rules.
First, and dumbest, solder the batteries together POSITIVE to NEGATIVE. The positive terminal has the bump on it, just like a regular AA. I laid the batteries out side-by-side, clipped the leads together, and soldered. Then just fold the mess together as tightly as possible and put a bit of tape on it to hold it together.
Step 6: Solder the New Batteries Into the Casing
Then, when you have the pack together, the POSITIVE lead goes up into the case, the NEGATIVE lead is soldered to the tab at the bottom of the case, near the four fragile wires.
It's a major boo-boo to get that wrong, so check it a couple of times.
As to how you get the battery tabs soldered to the stubs, all I can say is, I did the one in the middle of the casing first, folded up the tab, and then did the one at the bottom. The tabs need to lie nearly parallel to get a good solder join -- but then you can just bend the excess out of the way.
For what it's worth, the standard advice is, don't overheat the battery when you do this. How you'd know the battery is overheated, don't ask me. Anyway, the goal is to get solid solder joints between the battery tabs and the stubs of the tabs that are attached to the circuit board. No style points -- any way you can manage that is OK.
Step 7: Re-assemble
Insert the works into the case. DO NOT FORCE IT. The picture shows the proper orientation. (Forgot, didn't you? I sure did.) If in doubt, look down the top of the case, and the rod that holds the toothbrush will be centered in the hole if you have the whole works oriented right. Took me a few tries.
Now, here's where you may break one of the four small wires. (I did, and just soldered it back into place).
The hardest part of the entire deal is re-assembling the bottom. Hold the toothbrush upside down by the case, assemble the parts (with the "turning" part of the toothbrush bottom in the open (one-eight-turn-askew) position. What you have at this point looks like an exploded diagram of the bottom of the toothbrush. Make sure the four thin wires look like they are resting comfortably. Now hold the charger wrench facing downward, engage the upside-down toothbrush with the wrench, gently compress the mess, and turn it back one-eighth turn to tighten.
If all goes well, hey, that's it. If not, it'll take you three or four tries (as we did). We (my dad) broke one of the wires at that point, had to solder it back -- might be worthwhile taking a look at those before you start this step, just in case.
But all's well that ends well. Plug in the charger, put the brush on the charger, and see if it'll charge. Blinking light? All is well. After a couple of minutes, you can briefly turn it on to verify that it works. Then let it charge.
Step 8: Epilogue
Dispose of the NICD batteries as toxic waste, please. That's what you're supposed to do, and that's why the case opens up in the first place -- you're supposed to pull the batteries before you toss the device.
Bottom line: $5 worth of batteries, $3 shipping, and an hour of labor saves a $90 toothbrush. No idea how long this will last, but it seemed worth the gamble.
Finally comments: Probably should have replace the O-ring seal at the top while I was at it.
And, if you're going to be photographing your toothbrush for viewing on the internet...
...Clean it first.