Bill, can you elaborate on your setup. The way you show the drawing it appears as if you actually have 36 volts per "leg" vs 24 volts. I may be misunderstanding the drawing, but I doubt that is the case.
Either way, the issue with series connections is that you have to ensure all in-series batteries are balanced. That is one of the main reasons to limit the number of batteries connected in series, and is a strong incentive to go with 24-volt batteries if possible.
I know that the Fireflys are 12 volts.
Phantom, A54 #44