DJI FPV – Battery Breakout Mod Development

Description

Hello my name is AirCruiserFPV and I am attempting to mod/recreate the DJI FPV battery to use regular 6s Lipo batteries. (2022) Below is my development journey to the end product that I am now selling.

Why this project exists

DJI’s FPV intelligent batteries are expensive and limit flight time to roughly 8-15 minutes. Because the battery communicates via a proprietary protocol with the drone, you can’t just plug in a standard 6S Li-Po/Li-Ion battery. No third-party options were available, little community progress, plenty of motivated pilots. That was the starting point: to build a path to fly DJI FPV with “normal” batteries without hacking the drone’s firmware, while maintaining full in-goggle telemetry.

Early experiments: separating the “brain” and the “body”

The first phase was exploratory: open the smart battery pack, carefully split the BMS board from the cells, and try to make the cell block “modular.” That worked… until it didn’t. The BMS remembers charge history and counts current; if you swap cells, calibration breaks, and the drone flags battery faults. Lesson learned: a purely mechanical swap wasn’t enough. The communication had to be understood and mediated. Easier said than done…Finding the wire to pull: communication, not guesswork.

Finding the wire to pull: communication, not guesswork.

First, the hardware layer of communication had to be clarified. Rumors said, “It’s CAN.” Measurement said otherwise. Probing the battery connectors and unmasking chips on the DJI board revealed an RS-485 transceiver. Interpreting the lines exposed DJI’s DUML packets.
That unlocked reading traffic but not acceptance. The authentication remains opaque and encrypted; there was no realistic route to clone it wholesale. The breakthrough was to forward authentication to the original board when needed, then transparently mediate the live telemetry the drone cares about. In practice, this means a targeted, on-the-fly modification of specific battery data. At the same time, everything else passes through untouched, from the breadboard to the field-worthy board.

The first working prototype was a chunky per board:

Step down the 6S voltage, utilize RS-485 communication, parse DUML on a high-speed MCU, and ensure the DJI board remains integrated at the right moments. While it functioned, the cabling was chaotic, creating a rather disorganized appearance. From that point, we transitioned the electronics to a compact custom PCB featuring a proper user interface and a small enclosure that can be 3D-printed. The STL set—including the case, cover, LED light guides, and TPU buttons/feet—makes the package durable enough for everyday use.

What the Breakout Board does for pilots

You can use standard 6S packs with your DJI FPV drone while maintaining the familiar start-up and OSD behavior. The board ensures compatibility, securely bridges authentication, and provides reliable telemetry even when using custom packs.

The Battery Breakout Board features an onboard UI and in-goggle feedback, equipped with a compact display and three tactile buttons for quick setup and pack selection, even while wearing gloves. In the goggles, you have the option to customize how telemetry is presented in the following ways:

DJI-style percentage view:

The drone displays a familiar remaining percentage field, derived from the breakout board’s capacity tracking or preset calibration.

Classic FPV voltage view:

Alternatively, the OSD can be switched to show live pack

voltage (×10 format, e.g., “243” = 24.3 V), just like traditional FPV gear.

This flexibility enables you to maintain DJI’s standard appearance during casual flights or switch to raw voltage readouts for a more straightforward FPV experience. In either case, the data is transmitted directly through the goggles, with no additional modules needed.

Software at a glance

The firmware is where the bulk of the functionality resides, reliably parsing and mediating DUML, managing edge cases, and displaying battery status so you can focus on flying. The software offers three distinct modes for operating the board:

VreeMode (Voltage-based, zero setup):
Fly with any compatible 6S Li-Po or Li-Ion battery without the need for calibration. The display indicates pack voltage, current, and used capacity since power-on, while the goggles show voltage in the percentage slot (×10 format). Flight time estimation depends on your voltage management—avoid dropping below approximately 20.0 V on Li-Po batteries and around 18–19 V on Li-Ions, as DJI’s fail-safe will activate near these thresholds. This setup is ideal for using ad-hoc packs or conducting tests..

FlexMode (Quick capacity adjustment):
For consistent percentage and time-left readouts, you can set the pack’s nominal
capacity on the device in seconds (±100 mAh steps). Ideal when you rotate through
different 6S packs.

Battery Presets (6 slots with live calibration):
For your “main” packs, record a discharge curve once per cell type/age group to get steadier % and flight-time estimates. The board guides you through a hands-off calibration with the drone idling (~0.8–1.0 A draw). Expect roughly ~1 hour per 1000 mAh for a complete characterization; automatic cutoffs protect both Li-Po and Li-Ion profiles. After that, select the preset and fly. The OSD shows both % and voltage
(× 10).

What it took to get here (a condensed timeline)
2022 — First tests: Teardown, modular cell-swap idea, proof-of-concept flights, and
the discovery that the BMS’s current-counting makes naïve swaps unreliable.

Late 2022 — Protocol work: Identify RS-485, decode DUML framing, log thousands of
messages, and validate a hybrid approach.

Late 2022 – 2023 — Hardware iterations: From perfboard to a purpose-built PCB and
printable enclosures; field testing with different cell formats.

2023 – 2024 — Refinement: UI/UX polish on the board, preset management,
calibration workflow, and documentation for safe operation.

2024 Finished product: Beta phase, certification/compliance and finished
commercial product

Who it’s for
Freestyle pilots who want to break out of single-vendor battery lock-in and get
cheaper batteries. Long-range pilots who want to use Li-Ion batteries to increase their flight time. Tinkerers who like the idea of selecting the right chemistry (Li-Po vs. Li-Ion) for the mission while keeping DJI’s ecosystem conveniences.

There is a cutoff voltage for the DJI FPV drone and prevents one using the full capacity of the Li-ion cells. But that doesn’t mean there’s no benefit. With the Samsung 50s INR21700, one can probably use around 4000 mAh out of the 5000 mAh. That’s about twice as much as from the original battery. Because of the higher weight the flight time doesn’t quite double, but one can still get about 1.7 times more flight time compared to the original batteries.

With the Molicel INR21700 p42a (4000 mAh), one can get about 1.5 times the flight time compared to the DJI batteries. With the smaller Molicel INR18650 p28a (2800 mAh), one can still beat the DJI batteries however, the difference really isn’t that big anymore.

Safety, responsibility, and common sense
High-energy cells can be dangerous. Use high-quality packs, stay within sensible current limits (continuous ≥ ~10 A is recommended for battery builds), insulate connections properly, and avoid deep discharge.

YouTube: https://www.youtube.com/@AirCruiserFPV

Discord: https://discord.gg/Yfan8F3epY

Email: aircruiserfpv+hackaday@gmail.com

Thingiverse: https://www.thingiverse.com/thing:5715815

More of my development work is covered here:

https://hackaday.io/AirCruiser

You can purchase my completed board below.

It has been thoroughly tested and ready to use!