When you connect two battery packs in series, you are essentially creating a higher voltage battery pack.
Im not going to drive into detail on this topic just to keep things simple.

Things to remember when creating a battery in series connection:

1. make sure all the batteries in question are the same brand/make.
2. make sure both lipos have been used the same amount. Its best to work with brand new batteries
3. make sure the batteries have the same Mah ( milliamp hour )
4. of course the C rating ( discharge ) must be the same as well

If you use batteries with different chemistry for example a 25C or 30C, you could run into trouble at high power demands as the lower (25C) battery could dip below minimum voltage as it tries to keep up with the higher power battery.

 

 

How do you create a lipo battery in Parallel Configuration? Click here to find out