I’m upgrading from a quadcopter to a hexacopter which means my battery amp draw goes from 64 amps to 96.
The current battery I have is 5200mah with a 10c rating. (54 continuous amp draw. 20c (104amp max.) I know this is not ideal but it works fine. If I upgrade to 6 rotors I was thinking about getting this battery (https://hobbyking.com/en_us/turnigy-graphene-8000mah-4s-15c-w-xt60.html). It allows for 120 continuous amp draw. I don’t want to just put the old perfectly good battery on a shelf, if I put both batteries in series for a total of 13200mah, would that work even though the 5200mah battery only has a 10c rating? Would the 15c battery take most of the load off? The 8000mah new battery is 4s and 5200mah old battery is 3s.
Firstly you CANNOT put a 3S and a 4S in parallel, the terminal voltages are different and the 4S will try to charge the 3S with a high current which will destroy or worse the 3S
You can put batteries of the same S configuration in parallel with different C (discharge) ratings and as you suspect at those times when your hex draws a high current (rapid climb etc.) the higher C rated battery will produce more power. I don’t see this as an issue at all
Hop this helps
This would give you a terminal voltage of 25.9v (nominal) and about 29.4v (fully charged) and the first thing to do is check your ESC’s and Motors can handle this power, which I doubt but not having knowledge of your set-up I should not comment any further on that
On an electrical point of view, there is nothing to stop 3S and 4S being used in series. The big difference in C rating and capacity (mAh ratings) will cause an uneven discharge rate between the batteries which you would need handling.
FWIW my suggestion would be to get/use the Graphene 4S 8000mAh 15C (120A burst) on the hex (two of the same in parallel if you need more flight time) and use the 3S for something else.