I should introduce the individual boards. This is the Rev1 Vmon.

That 8mm hole on the left bolts to the battery positive terminal post. With the cable lug immediately under the pcb, and the battery below that as the plated through pad won't support 50A.
The flying lead to the left goes to the battery negative post.
The green phoenix plug upper left is an optically coupled board enable, so the mco can turn the vmon on when its actually in use.
There is a temperature sensor thermally close to the battery positive post
there is a small SMPS module to convert the input to 5V. It gets enabled.
bottom left is a 16 bit delta sigma ADC to measure the battery voltage
In the middle is the ESP32 module, with built in WiFi
On the right hand end is an array of balancing resistors. Spread out to allow heat dissipation
There is another temperature sensor to allow the board to switch the resistors on and off if they get overly warm.

Once built and tested, I sprayed the boards liberally with PCB acrylic for protection. I put painters tape over the battery pad, USBC connector and the phoenix socket first. Then I bolted some 1mm bare FR4 PCB top and bottom for mechanical protection. Before mounting in the mower I added duct tape around the 4 sides. With a hole in the tape for the enable plug and the battery terminal bolt.

Its the vmon's job to report battery voltage and temperature to the mco when polled. mco will tell vmon when to turn on the balance resistor if and when appropriate. Vmon will modulate the resistor on-ness if the resistors get too hot.

In this design each individual battery balances its own internal 4 cells. The VMONs permit balancing the 4 individual batteries to each other. 

Vmon responds to a suite of short serial commands either from the serial debug port or from WiFi to assist debug, do calibration, or change internal NVM constants such as ADC gain and offset, partner board MAC addresses and the like.

The set of serial reads and write commands for the board are documented in the source SW file for the board. More likely to stay current that way.

Thats all in the github repo, along with board schematic, both pdf and kicad, gerber and layout files.