You can bring dead batteries back to life after a failed firmware update without the help of Pylontech Support. If you turn on the small main switch while holding down the red start button, only the boot loader starts.
First you download the package with firmware and the flash program:
https://www.effekta.com/download/firmwareupdate-for-us2000c-3000c/
Unzip “Firmware update Pylontech US2000C_3000C V3_0.zip”.
Turn off the battery
Call “Update Tool.exe” in the “Upgrade Tool V1.0.9” folder
Choose serial port
Leave baud rate 115200
Click Immediate Update
click Connect
click Browse
Select firmware file: NT1.8+ST2.8.zip
(If you know what you are doing, you can also choose bin-files,
e.g. Us_c_Nt_V1.8_Crc.bin for the newer US3000C)
Start bootloader (press and hold red button and turn on main switch)
program
When finished, turn off the main switch, turn it on again, press the start button.
If “Unknown Input String” comes up when you click program, unfortunately you can’t select the
zip file (e.g. NT1.8+ST2.8.zip) with Browse, but must first unpack the zip and
select the appropriate bin file (e.g. Us_c_Nt_V1.8_Crc.bin).
NT1.8+ST2.8.zip