[Patrick]

I wouldn't suggest doing it, but it would be interesting to see what it actually would do in the real world. As the 2550's start losing voltage the 3250's should charge the 2550's back up a bit, since voltage between parallel cells should be even. Could have an unhappy ending though.

I have seen strange lipo setups used before with no issues though. 6 cell nimh (I think IB4200's) in series with 4900 mah 2s lipo. 4900 mah 2s in series with 4000 mah 3s of diferent C rating and brand. 25c 5000 2s venom pack with venom 4000mah 20c 3s pack, and a couple of others similar to that. I think the main thing is not to discharge the packs to far, 5 min races didn't hurt them.
Still don't recommend it though, especially when going for maximum runtime.

Do the packs need have certain dimensions? Can you fit 2x 3s 5000 - 6000mah packs in series.