Oh yawn yawn. This has been discussed endlessly. If you are too stupid to read the flight manual of an aircraft then what do you expect? The manual states perfectly clearly that you should not take off with a flat battery.
I think the above is grossly unfair. The checklist only said that "start the other engine normally" or words to that effect, not "WARNING! The other engine must be started using on-board power to ensure the battery is working". Looking at how the various parties reacted to this particular incident it is perfectly clear than no-one anticipated that particular failure scenario - and the fix also was a MSB, not just an update to the checklist. Yes, ultimately poor checklist discipline was the last hole in the cheese, but the root cause was a design flaw that now has been fixed.
Ultimately the DA42 is a new airframe, and while I am sure that there may be one or two flaws still to come out, it has a commendable safety record.