1. What’s B0B?

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.

B0B does not work with DJI mini2.

Let’s start by a video to see B0B running: https://youtu.be/pL0dGoH2AC4

To use B0B, the Mavic Mini firmware version shall be 1.0.0400 or below. Should you want to keep the advantages of the 1.0.0500 firmware with manual settings of the camera in video, just search for “DJI firmware module mixing”

The battery type inside the firmware shall bet set to type 2 or 3 (which means just a warning on the screen and a beep in case of low batt and no RTH. (you are just warned). Type 0 works too without any warning. When left in Batt-Type = 1; the drone won’t boot (error: “not genuine battery”)

2. What does it do?

Obviously there is some electronics behind this.

A PIC12F1840 microcontroller 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.

With DJI fly up to 1.1.15, 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:
804,7 °C ==> means 8,047 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 10%. Just enough to trigger the low batt warning ;-).

The latest version DJI Fly 1.1.6 and above does not display anymore the voltage on the main screen. You’ve to go to “…”, “security”, “battery” to get it:

You'll have to fly "with tension" reading the total voltage of the batt. Don't go under 6.5V 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!

3. Which battery?

Any 18650 cell with a discharge rate of 15A continuous and 20 A peak should do the job.

If you want to fly with the genuine cells, buy two Samsung 2500mAh INR18650 cells. They can be found for 10€ on ebay ;-)

The Sony VTC6 3000mAh are an excellent candidate too. They are few grams heavier than the SAMSUNG but they end at 101.4 grams (all included B0B, cells, 3D printed parts…) which keeps the Mini right under the 250 grams’ limit! 30 minutes of flight time can be achieved with those cells.

The battery is attached to B0B with a "sliding" 2x3pins connector. You can use a single B0B and own as many batteries you like.

the battery can be un attached and charged from an external charger using the same connector B0B is attached to it + the middle point to balance it... The charger you see on the picture above is a very cheap way to charge your cells. It is described here: https://www.thingiverse.com/thing:4550431

Some current (in the range of 2mA) is drawn by B0B when connected to the battery, so after usage, B0B must be removed from the battery. There is no protection for undervoltage. At 2mA, a full battery of 2400 mAh will lose half its capacity within 25 days, so please remove B0B after usage!

To use it just connect B0B to the battery. Then  connect B0B and its battery to the Mini.

In flight, it is mandatory to secure the battery to the drone. Use the 3D printed lock that will prevent the battery to slide back and self-disconnect… (with a crash of the drone).

Boot your RC, boot your mini. The LEDs under the Mini shall start with only one LED, then after few seconds display a correct voltage (all LEDs ON for a fully charged battery).

When the Mini will be recognized by the DJI fly application, the camera view shall display the % of charge and after a tap on the screen the “temperature” of 820 °C or so for a fully charged battery!

4. Can I buy one ?

First of all, I strongly advise you to read the complete read_me file .

I hope you will like doing this little project and experiment with batteries on your mini.

If you want to build one, use cleverly your B0B, do not go to low in terms of voltage and use B0B at your own risk repecting the regulations, I cannot be taken for responsible if you damage your drone nor if you create an accident.

I can provide B0B in several forms according to your needs:
- microcontroler alone
- microcontroler + PCB
- complete kit all components + connector for one batt + some 3D printed
parts (lock + centering)
- ready finished B0B in flight tested + connector for one batt + some 3D
printed parts (lock + centering)