Turn 18V Bosch Battery Into USB-C Powerbank

Bosch power tool batteries are pretty good at powering power tools. But sometimes, you don’t need to drill a hole you just need to charge your phone.

So, instead of letting that perfectly good 18V battery sit around doing nothing, we’re going to give it a second career: USB power bank.

The idea is simple. We’ll take a Bosch 18V battery, feed it into a small custom PCB with a DC-DC converter, and turn those 18-ish volts into a nice, civilized 5V.

The PCB will provide two USB-C female connectors, allowing us to power or charge two devices at once.

No giant power station, no complicated electronics, and no need to sacrifice a perfectly good power tool.

Just an 18V battery, a handful of components, and a small PCB that basically tells the battery:

“Calm down. We only need 5 volts.”

This project is directly linked to a previous project "https://www.instructables.com/Swiming-pool-One-Way-walkie-talkie-or-Rather-Swimi" were i use a similar concept to power a raspberry pi

My original project was sponsored by JUSTWAY an I could not have had the idea for this project without them

1. 3D printer
2. 2x USB-C Breakout Board (like this one)
3. 2x Straight PCB connectors (like this one)
4. Soldering iron + solder + about 15cm black & red wire
5. 18V Bosch battery
6. PC with PCB design software (i am using KiCAD)

The PCB is designed to slide directly onto the Bosch battery, using two spring-style PCB contacts like the ones shown below. The contacts fit into the battery’s terminals and provide a simple, detachable electrical connection, no need to modify the battery itself. All files for PCB Manufacturing and the files for the 3D printed parts can be fond on my github.

Once the 18V from the battery reaches the PCB, it is fed into an MP2338 buck converter. This little chip efficiently steps the battery voltage down from roughly 18V to a stable 5V, which is then supplied to the two USB-C connectors.

In the pictures associated with this step, I have attached the most important parts of the datasheet of the MP2338 chip that converts the battery 18V down to 5V to allow us to design the PCB around it.

If you have never read an integrated circuit datasheet, you can skim it (you can find it here). But here are the highlights (for this particular application). The first picture I took from the datasheet is the "typical application" circuit allowing us to see the number of components and and a rough idea of the values of the components that you will need. In this first picture, you can already see that we can expect a power efficiency of over 90% even if we draw power upward of 3A (which is not exactly fast charging but less of a big deal when we talk about a portable battery).

The second picture shows a detailed table of some combination of resistor and capacitor values to get the value of output voltage that you want (I chose the combination for 5V output voltage for USB compatibility).

Beyond those pre-computed values, you can, of course build something a little more custom using, for example the different equations (like the one on the third picture) in order to customize the characteristics of your DC-DC converter. This is the reason why I did not include the USB connectors on the main PCB because you might want to tweak the output voltage for other application !

The circuit I designed is essentially the exact reference circuit shown in the MP2338 datasheet, with the appropriate component values and layout adapted to this application.

I had the PCBs manufactured by JLCPCB (not sponsored, just a company I used for this project.) with the assembly of all SMD components, the THT connectors where soldered on by me.

In other words: 18V goes in, 5V comes out, and the expensive electronics in your phone remain considerably happier.

This first version is really more of a proof of concept than a finished product. It works, but the MP2338 is limited in terms of output power, so charging a smartphone with it will be rather slow.

The good news is that the basic design is already there: the battery interface, USB-C connectors and overall PCB layout can all be reused. Designing a second version with a higher-power, more modern buck converter would be relatively straightforward and could turn this little adapter into a much more capable charger.

For now, though, it proves the concept: an 18V Bosch battery can indeed become a USB-C power bank.