As someone who spends all my time at work connecting things in series: **Don't!**

Moreover, don't connect anything but resistors in series unless you absolutely have to.

What will happen is that one ESC will draw ever so slightly more current than the other despite your best effort to keep them equal. Said ESC will subsequently receive less voltage over it due to the series connection. To compensate, the ESC will try to draw more current, and this creates a positive feedback loop with it hitting undervoltage lockout. This is where the problem starts and is true for just about any regulated power supply. When it does, it stops drawing current but the other ones don't, pushing current though the one restarting and reversing the voltage across it (a bit depending on how much inductance you have in your circuit, but if the inductive spike won't kill it immediately, the new DC voltage across it will anyway), hopefully shorting it out. Once shorted, all the others will now have n/(n-1) higher voltage than before. This will continue until all have failed in a spectacular manner. If it does not short, you will have 400 V DC across it and possibly a flashover. Both are very unfavorable.

You can have bypass diodes and voltage clamps across each and try your damdest to make them equalize, but this is a loosing battle, uphill and in deep snow.

Please don't. Find another solution.