The TinkerCharge boards adds the ability to power your RTK project from a battery with charging via USB or 5V solar panels. TinkerCharge uses a BQ24074RGTT battery charger and an MAX17055 battery fuel gauge.  AdaFruit has an excellent tutorial on their board that uses the BQ24074RGTT. The BQ24074RGTT allows for simultaneously charging a battery and powering of the TinkerNav and accessory boards. Power can come from either the RP2040 or ESP32 USB-C connectors or 5V solar cells connected to the TinkerCharge board. A Li-ion battery is also connected to the TinkerCharge board. TinkerCharge makes building portable or solar powered base stations and hand held units easy. 

The MAX17261METD+T battery fuel gauge monitors the flow of current into and out of the battery and uses advanced algorithms to estimate the battery’s state of charge (% of battery remaining) as well as reporting real time current, voltage, and other battery information.


TinkerCharge is a small (25 mm X 16 mm) four layer board. There are two sets of 1X4 2.54mm header pins which connect to the TinkerNav board. The 1X4 header pinout is shown above. The VBUS pin brings power from either of the TinkerNav USB connectors. VCC is the output of the BQ24074RGTT charger and is an output to the TinkerNav board. The remaining two connections are SDA and SDL connections to the RP2040 so it can read battery data from the MAX17261METD+T.

 Additionally there are two 1X2 2.54mm JST style connectors. One of these connects to a single cell Li-Ion battery (we use two parallel Panasonic 18650 cells in our optional case). The second JST style connector connects to 5V solar cells. Many options are available for solar cells but we used three of these 160 mA 5V 140 mm X 45mm cells wired in the manner described here for our solar powered base station.

There are two indicator LEDs on TinkerCharge. The blue one shows that there is a power source, either USB or Solar, present that has sufficient voltage and current. The second green indicator LED is lit when the battery is charging. When this LED is off the battery is fully charged

Charging is limited by the BQ24074RGTT to 1.3 Amps. The charging limited is set by a resistor on the TinkerCharge board.

Schematic files for the TinkerCharge board are available in KiCad format from our GitHub page.  Schematics are licensed with the Creative Commons-Share Alike license. 


Software for the MAX17055 runs on the TinkerNav RP2040. A MAX17055_TR library is provided at our GitHub repository that implements all the required functionality for the MAX17055