Replacing Badly Corroded Battery Terminals in a Kids Toy
I recently came in to possession of an old Fisher Price toy. It was bought at a car boot sale for £3. A look at the bottom revealed it was made in 2003. It being that old was a good and a bad thing; the quality of an old toy like that is likely greater than that of a newer one but the corrosion could potentially have been given years to corrode the internals. I would have to see. I gave it a visual inspection. Physically it was in good shape. The wheel spun as it should, the button clicked as it should.. .
So with that, I decided to take it apart. The battery cover was already unscrewed. From the quick glance I took at the terminals, I was fairly sure I'd have to de-solder them and solder new ones in. Anyway, I took out the screws from the bottom and removed the cover. I was pleased to see the battery compartment was mostly isolated and that the main PCB of the toy had been saved from the leaking acid. Phew! I realised there were only 2 wires going to the battery compartment. Though that shouldn't have surprised me, I'm used to working on far more complex devices, e.g. laptop motherboards.
Desoldering the 2 wires wasn't difficult. I used some solder wick to clean the excess solder off of each tab. I didn't care about the terminals but I couldn't have removed them without damaging the battery compartment if there was a large glob of solder on each one. Once the solder was had been wicked away, I straightened the legs on each tab and used a pair of pliers to remove each of the 4 terminals. I pinched each one and pushed down on it. They shifted without much of a fight and I was able to grab them on the other side with my pliers and pull them out.
Unsurprisingly, they were complete junk. I found a pair of 10 positive and negative ones for £3.80 online. I was happy with the price and the fact it was dispatched by a local supplier - waiting for a small package like that to arrive from abroad could have taken weeks.
Next, a detour. I thought I'd best have a look at the power switch. The exterior was corroded and sure enough, when I put my multimeter over the pins in continuity mode, the reading was all over the place. 20 Ohms, 70 Ohms, 48 Ohms. A good switch should read almost 0. My solution was quick and dirty; I sprayed some contact cleaner in there and worked the switch back and forth a bunch of times. I gave it a few rounds and left it to dry. I left the window open and stayed away for a few hours. This isn't stuff you want to breathe in for any longer than necessary. Either way, when I came back, I tested the switch and was pleased to see it worked as expected. 2 Ohms. Nice! The switch was easy enough to sort but how about those battery terminals?
The new ones had since arrived and installing the first 2 was a walk in the park. I did them one at a time, sliding each in to place and holding it on the back with some electrical tape. I had to cut, strip and re-tin the wires as neither had usable ends but once done, I was able to solder the terminals down without issue.
How about the 2 pairs in the middle? They presented more of a challenge. My original plan had been to out a blob of solder in each corner and tether the 2 tabs together with a tiny run of wire. After giving it some thought, I realised that wasn't practical - the wire might get pinched somewhere, there would no doubt be excess, it wouldn't be very sturdy, etc. I eventually decided to use the excess from the legs of a diode - they're thick, sturdy and wouldn't get in the way as long as I was neat. To create the first pair, I put one of each terminal on the desk and tinned them up. I tinned the cut off leg of the diode with the help of a 3D printed holder. I used a heavy weight to hold the positive terminal down and tweezers to line up the leg; I soldered the end on and it was half-way done. I just had to do the same thing to solder the other side.
With that, one of the pairs was made. The soldering wasn't the best but it was together. I made another pair using the same method but reversed the position of the terminals. If I'd made 2 identical pairs, there would have been 2 springs at the top of the battery compartment, etc. To fix the poor solder work, I added flux to each joint, cleaned my iron, tinned it and added fresh solder. The joints were shiny and strong. Happy days.
There wasn't much left to do besides installing them in the toy and giving it a test but would they fit? Surprisingly, yes! Furthermore, they fit almost perfectly! There was a little resistance which served to hold them in place for testing. I installed the batteries and held the lid in place. I turned it on and nothing happened. I pressed the button and bam! It came to life! Crackly children's laughter filled the room and cut off abruptly. Quality. I spun the wheel and was greeted with more noise, flashing lights and a little jingle. I turned the toy off and it stopped doing anything. It came back to life when I turned it back on. Clearly, the switch was working too.
I removed the batteries and screwed the toy back together. Some pieces had fallen out earlier on but I'd set them off to the side. It wasn't hard to work out where they went. Once done, I put some T-7000 (glue) on the battery terminals and left the toy stood upright so it could set. I left it for several hours and when I later tried to shift the terminals about they were stuck fast. Result! I screwed the battery cover on and left it at that. The toy was fixed and ready for use. Result!
I really enjoyed working on it, it was an honest fix and a break from the norm. Usually, I fix laptop motherboards or upgrade computers, replace HDMI ports in games consoles and so on. I don't mind that work but the jobs I enjoy more are those that "aren't worth doing". For example, I fixed my dad's microwave a while ago using a part I took from one I found on the pavement. A waste of time but it's still in use... I 3D printed a replacement handle for my toaster as mine had broken off. 2 years later and it's still going strong... The other week I bought a humidifier upstairs. It was dead. 3 capacitors, 2 resistors and a SOP-8 chip later, it was working. I have already used it a bunch of time to help cool my flat.
The point is, none of the above were "worth" fixing but guess what? Not everything you fix needs to be. We live in a culture where unless you're monetising your hobby, you're seen as stupid. The parts of your hobby that are fun are usually the ones that don't pay. If they do, you've built yourself a job and it isn't fun anymore. I'm going to keep fixing stuff I find and doing the odd favour for people. Those jobs are more rewarding anyway.
Thank you for reading. As usual, the accompanying YouTube video is linked below:
(Repair Wins Blog - Post #7)
(June 2026)
