Issues with a Mega 2560+ESP8266

Hello all,
Having an issue with a Mega2560 clone that has an integrated esp8266 chip (MEGA+WiFi R3 ATmega2560+ESP8266, flash 32MB, USB-TTL CH340G, Micro-USB - RobotDyn) where the motors don’t move to their designated positions and move wildly around for a bit before stopping completely. When the board is powered by the battery and plugged into the computer it works fine but if I only power it from the battery the issue occurs. However, just controlling two servo with very simple commands works.

I’m running repeated inverse kinematic calculations for 18 MG996R servo motors which are controlled through two PCA9685 boards, and the battery is a 2C Lipo (at 7.8V when testing) which then runs through an SBEC with a max current of 20A. Everything worked fine on battery power alone when I used a plain arduino Uni. I’m aware it’s a dodgy board and will most likely transition to a plain mega board with a seperate esp8266 module but just seeing if I can get this to work as is.

Thanks

set esp8266 to bootloader mode with switch 7. then it will not start WiFi radio and you save 70 mA