Batteries on the Magic Trackpad last an amazingly long time. I would say about 6 months for my usage (on alkaline cells).
Nevertheless, eventually running out of batteries is always annoying so the other day I decided to power the Magic Trackpad using an USB cable.
This mod has already been documented on macrumors.com’s forum. My twist on it was to drill a hole in the stainless steel battery compartment cover instead of leaving wires exposed or drilling through the trackpad’s body.
Be warned that drilling stainless steel requires a lot of patience. You also need a drill that can rotate a slow speed and Cobalt drill bits. It is really important to take your time and not to drill for too long otherwise the heat will turn the stainless steel into super hard steel you will not be able to drill through.
In the case of that battery cover, being small it will get hot very quickly so I drilled for 30 seconds at a time, waiting a minute or two in between to allow for the piece to cool down.
It took me a whole afternoon to drill through the cover!
I used three 1N4001 diodes in series to step the voltage down a bit (from 5V to about 4.2V). You could use an extra two to bring the voltage closer to 3V, but the trackpad doesn’t seem to mind being powered by tensions over 3V (don’t try with more that 5V though) (I’m pretty sure Apple’s engineers used regulators to protect the trackpad’s internals).
In the process, I discovered that the positive end of the battery ersatz have to reproduce the shape of the + side of an AA battery. If the + end is flat it will not work. There is clever mechanism that doesn’t close the electrical circuit to prevent from damaging the trackpad if you insert the AA batteries in the wrong orientation.
- A small piece of soft wood, cut down to the dimension of two AA batteries in series
- Electrical tape
- A beer cap (for the negative pole)
- The positive tip of an AA battery
- A couple of 1N4001 diodes to step down the USB voltage
Bellow are a few pictures of my mod. Enjoy!