Mixing discharge rates on LIPOs

[FreeRider2RCnut]

Hopefully this won't go down as the stupid a$$ question of the year and I also hope this question hasn't been asked 10,000 times already cause when I searched I found no info. Anyway here is the question.

I have a lot of batteries and I have some big electric planes. I have some on 6, 8, 10 and 12 cels. Since I didn't buy all of the batteries at the same time I have several discharge rates, mostly 20, 30 and 40c. Is it safe to mix the "C" rating.

Can I use a 40c battery with my 20c safely?

[NormS]

I'm not a battery expert by any means, but here are my thoughts about this.

I think putting different C-rated cells in series is a bad idea because the lower rated cells could get overdischarged and destroyed. Your ESC can only sense the overall pack voltage and the higher rated cells will mask the lower rated cells.

I think putting different C-rated packs in parallel is OK, as long as all of the individual packs have the same nominal voltage (i.e. the same number of cells in series). You should never parallelize batteries of different voltages.

In both cases (series and parallel) the max available "C" is the smallest C of the combined group of packs.

That said, I myself would never consider mixing packs of different C ratings and/or different capacities. Lipo's are known to be touchy and to me its just not worth the risk of setting my plane on fire or ruining the batteries. I would like to hear from a real expert about this, however.