Fix bug in batteryBDC

[JamesHabben]

• the watts column was causing an index error on csv files where there were not enough columns
• check for 9 columns in source file; write error and skip file if less
• safely get watts value or '' if column isn't there
• lint error cleanup

[JamesHabben]

here is the error i got when running against josh's ios15 image. for reference

[21/439] batteryBDC [batteryBDC] artifact started
Reading batteryBDC artifact had errors!
Error was list index out of range
Exception Traceback: Traceback (most recent call last):
  File "ileapp.py", line 506, in crunch_artifacts
  File "scripts\ilapfuncs.py", line 477, in wrapper
    data_headers, data_list, source_path = func(Context)
                                           ^^^^^^^^^^^^^
  File "C:\Users\James Habben\AppData\Local\Temp\_MEI247162\scripts\artifacts\batteryBDC.py", line 47, in batteryBDC
    watts = item[18]
            ~~~~^^^^
IndexError: list index out of range