I'm sure everyone has had the experience of having the rechargeable batteries in a rechargeable appliance stop being able to be recharged. The most recent addition is my electric shaver. I'm not a big fan of them, but it's handy for me to save my skin by alternating between the razor and the shaver.
Anyway, I had replaced the batteries once before. I picked up a replacement battery at a Ham Fest or some such place. It worked for a while, but I got to thinking: why am I bothering with these odd-sized custom batteries when I've got plenty of rechargeables lying around?
Step 1: Take It Apart
No big deal ... open up the case. Right?
Unfortunately, the people who made this shaver decided that it was important to use Torx-like screws rather than some kind of standard Phililps-like one. Fortunately, the trick to these is to use a small flat-bladed driver that can seat between two points. In this kind of application, the torque on the screw is very small. Obviously, you're not going to get a rusted Torx off a car with a flat-blade, but for this, it works great.
Step 2: Remove the Battery and Charging Electronics
This particular shaver is a piece of cake. The case holds all the electronics in place so they just come right out. I just want the motor to stay in place which is the only thing mounted. I'd like to have been able to use the existing power switch but it would be easier to just add one later.
I also checked and the battery is 2.4V -- 2 1.2V rechargeable cells. The capacity is rated at 600mAH, so by using some meager 1,800 mAH AA batteries, I can triple the run-time ... as if that was ever an issue.
Step 3: Install a Suitable Battery Holder
I was looking around for my 3-cell AAA holder because I had in my head it was 3.6V (most cordless phones are), but since I only need 2 batteries, I had to scrounge up a 2x holder. For a different project, I have the bases for cheap battery-powered lamps. I cut apart the bottom with my band saw and scavenged one of the battery holders.
To mount it, I just drilled a couple holes in the holder and then used them as a template to drill holes into the front of the shaver. I decided to use the front so I could still use the beard-trimmer feature on the back and so the shaver would sit in its charging cradle (even though it won't be plugged in anymore).
Don't forget to find screws that are short enough that they don't hit the batteries when they're installed.
Step 4: Add a Switch
I found a switch that would fit right in the hole on the bottom where the AC power cord once went, but I would then have to modify the charging cradle so it would still fit. I went the lazy route and put the switch elsewhere. I simply glued it to the side of the battery holder.
Step 5: Wire It Up
To wire it up, the battery pack, switch, and motor need to be wired in series. Either the + from the battery pack goes to the switch or the - does -- it doesn't matter as long as you go battery-pack-to-switch-to-motor-to-battery-pack. In my case, it was more convenient to use the + side with the switch as both the + battery terminal was on that side and the existing wire on the motor was long enough to get to the switch, so I just drilled a hole through the shaver to hook it up.
Step 6: Put It Back Together, Add Batteries, and Start Shaving
Although annoying the Torx-like screws were the right length so I used them when I put it back together. I put in some NiMH rechargeable batteries and switched it on and it works just like it did before.
To recharge the batteries, I just use my existing AA charger. I could have kept the charging circuit in the shaver, but I think it's kind of a waste to let the shaver charge all day just to use it for a few minutes in the morning. Admittedly, it's "only" 2 watts, but now I have some neat parts to play with too.
I'll take the existing NiCD rechargeable pack to Radio Shack to be recycled.