We bought the “Fisher-Price Thomas & Friends ride-on Train” for our toddler and after some time the battery stopped charging.
It uses a Power Wheels 6V 2400 mAh NiMH battery (Model No. 1102822518 / Part No. 3900-8218).
Apparently this battery was fairly unique (and problematic) to this toy and has since been discontinued.
I of course did not want to have to scrap an entire power wheels toy that worked just fine except for the battery.
One thing I will say about it though is that it’s surprisingly repairable. I was able to open it up just by removing 4 phillips screws.
From what I gathered, the circuit board is what makes this battery unique. It allows charging the NiMH battery via micro-usb instead of the typical power wheels charger.
All of the wires seemed fairly self-explanatory. Except for two small additional wires coming from the battery pack.
Well, it turns out these 6v battery packs are just 5 rechargeable AA batteries strapped together. The wires were just going to a small thermistor to measure the temperature of the batteries as a way to gauge much it’s charged.
After that, all I had to do was desolder the battery pack from the board, buy a replacement, solder it to the board, and tape the thermistor to the new pack. Then seal it all back up and I was good to go!
I did come across a service that seems to this for you but it turned out to be fairly straightforward to do it myself.