Mavic Mini : B0B (fly any Battery with no BMS)

B0B is a very simple way to fly your Mavic Mini without the DJI genuine battery but with the telemetry of voltage available on the RC. B0B is not a battery, it's rather a cheap platform to experiment with any battery you wish.
B0B is able to communicate with the ESC board of the drone giving it just enough information to be accepted at boot and to monitor the voltage during the flight.

Obviously there is some electronics behind this.

A PIC12F1840 microcontroler will emulate the I2C traffic needed by the ESC board of the Mavic mini to start the drone and to collect telemetry information.
The voltage of the cells is acquired by B0B via a resistor bridge.

The total voltage of the batt is displayed into the Mavic Mini temperature field. This is done on purpose just to remember you flight with B0B and not genuine battery.
The voltage is displayed like this :
820,0 °C ==> means 8,200 V

This value is then divided by 2 and displayed into each cell gauge
The battery remaining capacity is estimated based on the total voltage and displayed on the screen. The estimation is NOT accurate and is clamped to a minimum value around 11%. Just enough to trigger the low batt warning ;-)

You'll have to flight "with tension" reading the total voltage of the batt. Don't go under 6.6V or the batt can be damaged (and the drone may lose power and eventually crash)

To be clear, as its name means B0B is a battery with no BMS.
You cannot use it to charge the batt from the DJI charger nor from the USB plug from the drone.
B0B is "stupid". it just fools the DJI firmware giving it just enough information to start the drone and display voltage . That is !

The battery is attached to B0B with a "sliding" 2x3pins connector. You can use a single B0B and own as many batteries you like. Two Samsung 2400mAh 18650 cells can be found for 10€ on ebay ;-)
the battery can be un attached and I charge it using the same connector to attach it + the middle point to balance it...
Some current (in the range of 10mA is drawn by B0B, so after usage, B0B must be removed from the battery. There is no protection for undervoltage.

To use B0B, the Mavic Mini firmware version shall be 1.0.0400 or below.
The battery type inside the firmware shall bet set to type 2 or 3 (which means just a warning on the screen in case of low batt and no RTH. (you are just warned)

BTW, why placing it on thingiverse? just because there is a 3D printed lock mechanism to avoid a disconnection of the batt ...

The most difficult part to source is the battery connector. I found a way to DIY a female battery connector.

If you look on the picture, the genuine lyre (golden one) offers 4 contacts to the male pin. I simply extracted some female lyres from a 2mm pitch square pins connector and placed them two by two inside a 3D printed case. It's a pain to solder in place and the best way is to use a male connector or at least a male pin to keep the female in place while soldering.
Be patient, the result is excellent, we get the same four contacts to the male pin. Insertion into the male connector requires a lower but good enough amount of force than with the genuine one.
If the MM draws 10A, this gives 5 A per pin as Vdd and GND are duplicated which turns into 2.5A per lyre and 1.25A per contact... It should do the job !

Should you be interested to build one, just PM me, but you have first to fully understand what's written above ;-)