Introduce battery_info uORB message for static data like the serial number #24960

MaEtUgR · 2025-06-03T12:18:47Z

Solved Problem

When tracking battery use across multiple flights and vehicles using the serial number from flight logs I found that:

The serial number, that we currently have in battery status is a uin16_t which is too limiting for my use case and likely also others. I found that this periodic battery DroneCAN message
and the BATTERY_INFO MAVLink message have settled on a char[32].
I asked in a thread about this here: Common: rename SMART_BATTERY_INFO to BATTERY_INFO and add SOH mavlink/mavlink#2070 (comment)
The serial number of a battery doesn't change so it should not be logged at high rate. This gets more important with a char[32] type because of the wasted space. We need a low rate battery info message for all such static information.

Solution

Add a battery info uORB message and have the id field match the value of battery_status.id to correctly keep track across topic instances.
Have a char[32] battery_info.serial_number field for the unique battery identifier and adjust the upstream drivers to use it.

Other static fields I plan to sort out and move to the battery_info message separately from this pull request.

Changelog Entry

Introduce battery_info uORB message for static data like the serial number

Test coverage

EDIT: I just successfully tested this latest version with a UAVCAN Tattu battery (I'll make a separate pr for the message parsing of that one):

github-actions · 2025-06-03T12:25:07Z

🔎 FLASH Analysis

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px4_fmu-v6x [Total VM Diff: 512 byte (0.03 %)]

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Updated: 2025-06-16T17:33:18

mrpollo · 2025-06-03T13:32:19Z

This is something great to track down in Flight Review as well!

docs/ko/msg_docs/BatteryStatus.md

hamishwillee · 2025-06-03T23:59:25Z

msg/BatteryInfo.msg

+uint64 timestamp # time since system start [us]
+
+uint8 id # Must match the id in the battery_status message for the same battery
+char[32] serial_number # Serial number of the battery pack in ASCII characters, 0 terminated [@invalid All bytes 0]


Metadata moved to appearing first as per your original suggestion. It makes parsing easier.

Let's add a description

Suggested change

uint64 timestamp # time since system start [us]

uint8 id # Must match the id in the battery_status message for the same battery

char[32] serial_number # Serial number of the battery pack in ASCII characters, 0 terminated [@invalid All bytes 0]

# Battery information.

#

# Static or near-invariant battery information.

# Should be sent on request or streamed at low rate.

uint64 timestamp # [us] Time since system start.

uint8 id # Must match the id in the battery_status message for the same battery.

char[32] serial_number # [@invalid 0 All bytes] Serial number of the battery pack in ASCII characters, 0 terminated.

Totally! Thanks for the exemplary input, I'll adjust👍

Awesome. Made minor change above - the format is [@invalid <value> <optional description>]

I took over a version of your proposal in 9fc28fb481226b22b2a03733484d6934cef33f6b

I left away the on request part since I'm not currently aware of any mechanism to do that.

I left away the . after all the short descriptions(.)

msg/BatteryInfo.msg

src/modules/mavlink/streams/BATTERY_INFO.hpp

src/modules/logger/logged_topics.cpp

MaEtUgR · 2025-06-11T09:25:17Z

It's rebased on latest main and I addressed the documentation review 🙏

src/modules/logger/logged_topics.cpp

sfuhrer · 2025-06-11T12:04:38Z

msg/versioned/BatteryStatus.msg

@@ -1,4 +1,4 @@
-uint32 MESSAGE_VERSION = 0
+uint32 MESSAGE_VERSION = 1


This bump requires a translation. If you anyway want to move other fields over to the info message I would consider doing it here all in one PR to not have to do the translation multiple times.

I'm learning 💡 Let me check.

If you anyway want to move other fields over to the info message I would consider doing it here all in one PR

From a public interface standpoint this would make sense but I'd still like to avoid it since if I start to sort out the entire message in this pr it will:
a) take a while to finish (this one already did)
b) explode in size and be hard to review and test

I'd like to work through in iterations. I can make the next one bigger if desired.

That was a big handful of boilerplate. Luckily Gemini helped me fill in the repetitive stuff... 😓
The important portion in the docs is the step by step guide here:
https://docs.px4.io/main/en/ros2/px4_ros2_msg_translation_node.html#updating-a-versioned-message
All changes are in the last two commits.

@MaEtUgR FMI did you find those docs understandable? It was hard to make logical and I didn't actually have to test this in anger so hoping we didn't miss anything.

docs understandable?

@hamishwillee To be honest I was in a hurry and skimmed twice to find just how I can do the translation. I couldn't follow 1:1 because the message did not have a translation before. I checked high-level what I need and took the useful example https://github.com/PX4/PX4-Autopilot/blob/main/msg/translation_node/translations/example_translation_direct_v1.h and compared it against the relatively simple https://github.com/PX4/PX4-Autopilot/blob/6b2b20bd6ecb18eb6d3380449dce1fc75f61ce2d/msg/translation_node/translations/translation_event_v1.h. The quickest for me would have been an example commit to an exclusive such change but the events one is mixed with other changes and I'm not even sure why it was done since the message looks exactly the same to me 🤔 TL;DR really good docs but on the verbous side for my particular case 😇

TL;DR really good docs but on the verbous side for my particular case 😇

Yeah, I've noticed that I'm leaning towards comprehensive but too long docs recently. Sorry!

If you find a good commit that works as a reference in future, let me know!

And thanks for the merge of the docs!

hamishwillee

Approving for my part. Though I hope my docs stuff goes in first in the other PR :-)

MaEtUgR · 2025-06-12T15:37:06Z

Though I hope my docs stuff goes in first in the other PR :-)

@hamishwillee Of course we merge your docs pr (#24789) first, I rebased 👍

sfuhrer

MESSAGE_VERSION in the battery_status needs to be be bumped to 1.

…AVLink and drivers I'm starting the separate battery info message because no char[32] should be published and logged at high rate and we need a separate battery info message for static information as discussed.

…info message

MaEtUgR · 2025-06-16T17:28:49Z

@sfuhrer Good catch! That change was mistakenly dropped during the rebase on #24789

see https://github.com/PX4/PX4-Autopilot/compare/3c3889c7aaf28aeb04eda59fb0a16185ecbdd859..32d5e4c083a51c6367635b29f7c5e844e8a85b8b#diff-ba1e5883c30b750699aaf7a0a5a4708cd928beffe108ff1cb58921b7b611d829L1-R7
Sorry for that 🤦‍♂️ I just fixed it ✅

src/modules/logger/logged_topics.cpp

MaEtUgR self-assigned this Jun 3, 2025

MaEtUgR mentioned this pull request Jun 3, 2025

Common: rename SMART_BATTERY_INFO to BATTERY_INFO and add SOH mavlink/mavlink#2070

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Support for CBAT uavcan message parsing #24973

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MaEtUgR mentioned this pull request Jun 6, 2025

BatteryStatus.msg - docs update #24789

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MaEtUgR added 8 commits June 16, 2025 19:26

Add battery_info message with serial number compatible with UAVCAN, M…

df0fe1c

…AVLink and drivers I'm starting the separate battery info message because no char[32] should be published and logged at high rate and we need a separate battery info message for static information as discussed.

batt_smbus: switch to battery_info.serial_number

33a6f01

smbus_sbs: switch to battery_info.serial_number

b901b28

batmon: switch to battery_info.serial_number

a45c286

uavcan battery: switch to battery_info.serial_number

9652611

cyphal: switch to battery_info.serial_number

8fc1c71

msg translations: sort headers alphabetically

2ced749

battery_status message: remove serial_number which is now in battery_…

046eb10

…info message

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-uint64 timestamp # time since system start [us]
-uint8 id # Must match the id in the battery_status message for the same battery
-char[32] serial_number # Serial number of the battery pack in ASCII characters, 0 terminated [@invalid All bytes 0]
+# Battery information.
+#
+# Static or near-invariant battery information.
+# Should be sent on request or streamed at low rate.
+uint64 timestamp # [us] Time since system start.
+uint8 id # Must match the id in the battery_status message for the same battery.
+char[32] serial_number # [@invalid 0 All bytes] Serial number of the battery pack in ASCII characters, 0 terminated.

		@@ -1,4 +1,4 @@
		uint32 MESSAGE_VERSION = 0
		uint32 MESSAGE_VERSION = 1

Introduce battery_info uORB message for static data like the serial number #24960

Introduce battery_info uORB message for static data like the serial number #24960

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