This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

How can used 2 2s lipo battery to make a 4s lipo battery ?

I'm a UAV lovers, and my drone used a 4s lipo battery. I have two 2s battery, I want to make a new 4s lipo battery by my two 2s lipo battery, so I take the 2s lipo battery in Series. But when I did it , my drone can't fly normal ,I don't know the reason?