This quote from vic7767 may be what you need to do:
The Firefly comes loaded with the default baud rate of 115K. The is a configuration time that will timeout after 60 seconds and no other changes will be allowed via input commands. Your first task is to change the Config timer from 60 seconds to forever (255). Power up the Firefly, establish a connection via your PC, type $$$ and receive the CMD prompt. Type in "ST, 255" without the quotes to change the Config timer to always on. Then type "SU, 115" to set the baud rate. Then type "---" to escape the command prompt. Now you should be able to monitor the charging data from your Roomba as I mentioned earlier.
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