Junctek Battery Monitor BLE protocol info

Tl;DR:

• Write 0x100 to handle 0x22 (UUID 00002902-0000-1000-8000-00805f9b34fb) to start receiving records as values change
• Write 0xbb9aa90cee to handle 0x25 (UUID 0000fff2-0000-1000-8000-00805f9b34fb) to trigger a once-off transfer of all parameter values

Data format

• Records are sent with a start byte of 0xbb and an end byte of 0xee.
• Records can contain one or more parameter values.
• Format is value byte 1 [... value byte N] followed by the parameter type.
• Values are packed BCD, parameter types are in the range 0xb0 to 0xf0.

ID	Paramater Name	Equation
b0	Battery capacity	x / 10
b1	Over-temp protection (C)	x - 100
b2
b3
b4
b5
b6
b7	Relay mode	0 = N/O, 1=N/C
b8
b9
c0	Volts	x / 100
c1	Amps	x / 100
c2	Protection delay sec	x = seconds
c3	Protection recovery sec	x = seconds
c4
c5	Over-voltage protection	x / 100
c6	Under-voltage protection	x / 100
c7	Over-current protection	x / 100
c8	Over-current charge protection	x / 100
c9	Over-power protection	x / 100
d0	Relay state	0=off, 1=on
d1	Charge state	0=Discharging, 1=Charging
d2	Ah remaining	x / 1000
d3	KWh discharged	x / 100000
d4	KWh charged	x / 100000
d5	Total run time	x = seconds
d6	Time remaining	x = minutes
d7	Impedance	x / 100
d8	Watts	x / 100
d9	Temperature (C)	x - 100
e0
e1
e2
e3	Under-temp protection	x - 100
f0

State of charge is not a stored parameter, but is calculated with (d2 / 100) / b0

Example

Record recieved:

bb 08 23 14 44 d5 09 99 99 d2 32 05 66 d3 24 ee

bb = start of record
08231444 = 1st param value
d5 = 1st param type (Total Run Time of 8231444 seconds, or ~95 days)

099999 = 2nd param value
d2 = 2nd param type (Ah remaining = 99999 / 1000, or 99.99 Ah)

320566 = 3rd param value
d3 = 3rd param type (KWh discharged = 320566 / 100000, or 3.20566)
24 = checksum byte
ee = end of record

Operation

• Write 0x100 to handle 0x22 (UUID 00002902-0000-1000-8000-00805f9b34fb) to start receiving records as values change This will cause the device to start sending records to the notification handle 0x2d whenever a parameter value changes.
  If there is no current flowing in or out of the battery, the only parameter that will be changing frequently is d5 Total Run time, which will increment every second - and if the output relay is set to OFF, you may not see any traffic at all.
  Many of the parameter values will never change without manual intervention (e.g. most of the b* and the c* configuration and protection settings) so these will not be visible without triggering a one-off dump of all parameter values.

• Write 0xbb9aa90cee to handle 0x25 (UUID 0000fff2-0000-1000-8000-00805f9b34fb) to trigger a once-off transfer of all parameter values
  This will cause the device to immediately start sending all the (unordered) parameter values once to the notification handle 0x2d if it is already sending notifications.

Perl Script

junctek.pl is a small Perl script that wraps gatttool to fetch all the parameter values from a Junctek battery monitor device once, and optionally publish them to an MQTT server.
(Note: gatttool has been deprecated for a while now and one day will disappear from distros)

Parameters can either be set in the configuration section at the start of the script, or supplied on the commandline. Commandline options override the script settings.

Usage: junctek.pl [OPTION?]

Options:
        -d, --device=MAC                Specify remote Bluetooth address
        -q, --quiet                     Don't print output
        -m, --mqtt                      Enable (1) or disable (0) publishing to MQTT
        -s, --server                    Hostname of MQTT server
        -u  --username                  MQTT username
        -p  --password                  MQTT password
        -n, --name                      'Friendly' name of device, MQTT topic becomes junctek/[name]/...
        -r, --retain                    Publish MQTT messages with retain flag

To publish to MQTT, you'll need the Net::MQTT::Simple Perl module installed.
If its not available as a native package for your distro, it can be installed from CPAN e.g.
perl -MCPAN -e 'install Net::MQTT::Simple'