I agree BMS powered by 12v supply is better.
My BMS is not wired via the ignition at all, it is totally independant and has seperate on/off switch allowing it to run when car is off to control charging. The zivan relay contacts may be a good idea and perhaps we can just use the contacts via the bms interlocks so it can detect when the zivan has turned off.
I also think a simple press to make button which allows a transistor switch to be activated which powers the bms, the transistor switch is then fed/kept alive by the bms which can cut the drive to the transistor when reqd killing it's own power supply.
I agree a RTC may be a good idea there are a few used with picaxe etc that we can use with pbpro
http://www.rev-ed.co.uk/docs/DS1307.pdf this can be on the same bus as the I2C temp sensors which saves pic pins. The more I2C stuff the better.
The I2C tempsensor serial numbers may be able to be stored several places.
1) In the master pic eeprom. But if you upgrade the software you would have to modify it to incorporate the temp sensor serial number data each time.
2) In the eeprom chip, this is then available even if master program updated.
3) In the RTC SRAM as above
Some other thoughts I had about Master Board V3. Some of these are Insight specific.
An ODBII connection so that data from the car can be displayed on BMS screen.
A BCM Interceptor (This is an RS485 interface specifically for the Honda Insight)
Return the last slave bus in the strings data to the Master, this gives us an easy check to see if the commands have been received correctly. So we have a loop. Out of Master to first slave, passed along slaves until out of last one and back into Master.