Rechargeable battery technology has come a long way since the days of NiCads, and the fact that many devices can now charge off USB power means that it is rare that any of our devices are out of power for too long. However, for a lot of older devices we are stuck with buying single use batteries, or rechargeables that are inconvenient to recharge when you are on the go. This is why I decided to try retrofitting a USB recharging lithium ion battery pack to an old GameBoy.
This hack depends on a little bit of an insight I had, and that is the fact that a lot of battery powered devices can run of a much lower voltage than the batteries that are put in them would seem to indicate. This is because, although AAA, A, C and D cell alkaline and heavy duty batteries are rated at 1.5V, their NiCad and NiMH rechargeable cousins are actually 1.2V. Since most battery powered devices will happily run of these rechargeables we can take a 20% drop in voltage and most things will be fine. This means that something like a GameBoy, that runs at 6V will happily run off 5V, which is the voltage output by a USB battery pack. So, to make this battery pack all that needs to be done is to design a USB battery pack that will fit in a GameBoy battery compartment.
To build this you will need a soldering iron and a hot glue gun. You will need to find somewhere to print you the 3D printed parts, and if you do it yourself you will need the necessary tools to clean them up. Also a screwdriver that fits the nuts mentioned below and a small pair of pliers will help in the assembly. I'm sure I've missed something I used here, but all of what I used will be found in the tool kits of most people who mess around with electronics.
Bought Parts
If you look around eBay and Alibaba you will find lots of small voltage regulation boards for USB battery packs. For this project I went with the HP-0051D pictured above. This is because this board works with 3.7V batteries (which seems to be the standard voltage for lithium ion batteries) and was slightly smaller than the width of the battery compartment door. This board seems to be mainly intended to be used as part of a USB battery back, and as such the output voltage is 5V. I grabbed mine off ebay for £2.50.
The battery I used was a 2000mAh KCR1410 and it can be purchased from Replacebase but it is chaper elsewhere. I got mine from Alibaba for US$2.40. It was originally intended as an upgrade for PS4 controllers. For some reason the battery came with a micro USB cable, which was odd because it does not have a USB port on it to charge it, but convenient as the charge board didn't.
The only other parts needed were two M3, 4mm length bolts, the corresponding nuts, two 3.2mm (6BA) circular crimp connectors and some wire (I just used some speaker wire I had lying around) and of course the 3D printed marts I designed. If you want to populate the positions on the regulation board that are there for charing and discharging LEDs you will need those as well, but this is optional.
Designing the 3D printed parts
In order to build the battery pack I needed 3 3D printed parts: 2 sections to slot into where the batteries go and a backplate to go into the GameBoy battery cover. I initially considered building the whole battery pack as a single part because it might be a more robust design. However in the end I came to the conclusion that it would be too hard to build, so I came up with a 3 part design: One backplate that would hold the battery and the charging circuit and two AA battery shaped parts that would be used to connect to the GameBoy.
I started by taking a battery cover that already existed in thingiverse (here is the original) and loading it up in OpenSCAD. OpenScad is an open source CAD program where you define the object in code, by adding and subtracting shapes from each other. As a programmer this felt very natural to me. I went ahead and added some space to the back of the battery pack to slot the regulator board and the battery into., and then subtracted the necessary shapes to allow them to be slotted in. I also made holes for the LEDs on the regulator board, a hole so that the micro USB connector could be accessed and put in supports so that the regulator board sat in place properly.
The two parts that would connect to the battery terminals were basically two hollow cylinders with parts cut away to allow the backplate to fit in with the battery on it, and holes for the nuts and bolts that would actually touch the terminals. I also added notches to the sides of these to stop them rotating inside the GameBoy. In hindsight I'm not sure that this was important, but it's there now. You can get the STLs here and the OpenScad code here.
Assembly
The first thing to do is to clean up the 3D printed parts. What you need to do here will depend on your printer. You may want to rotate the batteries so that they sit flat on the print bed. I will assume here that you know how to get good prints out of your printer.
While that is running it will be a good time to remove the full sided USB port from the regulator board. Use your preferred technique to remove as much solder as possible from the connection. Solder 6cm of wire to the positive and negative connections. The next thing to do is snip the connector off the battery and solder it onto the positive and negative terminals on the back of the regulator board, you may need to extend the positive wire a bit so that it can reach the positive terminal. Then thread the loose wires through the two upward facing holes and put everything in place to make sure it all fits before gluing. It should look like this.
If everything seems to fit together and you can plug in the the micro USB cable it's time to glue everything that has been put together up until this point into the battery cover section. If not you may need to clean up the 3D print a bit before continuing. In addition to gluing the battery and circuit board into place also glue the two wires that have been threaded through the two upward facing holes. Then thread the wires through the back of the backplate so that they will be inside the GameBoy when you put it on. Make sure that the positive wire comes out on the right and the negative on the left when the back of the backplate is facing you. If you have got the wires switched around inside the battery pack, you will need to switch them around again here, like in the image at the top of the page.
Next take the plastic sheath off two circular crimp terminal connectors and crimp them into the end of the wires. Then take a nut and bolt and bolt the terminal into the 3D printed battery parts, ensuring the left battery is on the left side, and the right battery is on the right side (the notches are meant to go into the corners). Also make sure that the connectors point into the GameBoy battery compartment because if they point any other way the backplate will not fit on properly. What you have now should look something like this
And that is the assembly pretty much done. To install it place the batteries sections into the GameBoy so that the tops of the bolts touch the battery terminals, as seen below, put the cover on and away you go.
Performance and final thoughts
The obvious question with this battery is how does it perform compared to real AA batteries with the drop from 6V to 5V. From my testing of the battery I can say that there is no noticeable difference between AA batteries and this battery. As for battery life, I tested this by taking the battery to a full charge and running the GameBoy with a game in place (so the game would run in "demo mode" and actually put some drain on the battery), with the sown down and the contrast high. I found that the battery lasted 12 hours in this test. Other tests have shown that a set of AA batteries will give you 10-30 hours of play time, so this does come in on the low end of that, but I think that the convenience of being able to recharge from any micro-USB cable, and the fact that you can play it while the battery is charging makes up for this.
So, I think that pretty much sums this up. I find that now I don't have to scrounge around for a set of AAs every time I want to play it I use the GameBoy a lot more now I just pick it up and play it. If I do another GameBoy modification it will probabbly be to add in a backlight, as the screen of these were pretty terrible. If I do this I will post an update on how the performace with the battery is impacted with the addition of a backlight o the screen. Also, if I ever get my hands on one I will let you know the running time with an EverDrive GB in there instead of a regular cartridge. But as always, thanks for reading and I hope someone out there takes some inspiration from this and uses some of the ideas here to bring new life into some of their old electronics.