Not sure why no place on google or elsewhere here has this info easy to find... so I eventually found it here:-
github.com
Here is the connector pinout:
As well as the meaning of all the pads on the back (not all board have these pads labelled - mine for example does not).

The SCL and SDA are especially useful - needed to reset the permeant failure flag using GitHub - o-gs/dji-firmware-tools: Tools for handling firmwares of DJI products, with focus on quadcopters.
WM220 Battery Intelligent Board
Tools for handling firmwares of DJI products, with focus on quadcopters. - o-gs/dji-firmware-tools
Here is the connector pinout:
Pin | Function |
---|---|
1 | RXD (UART receive) |
2 | PACK- (GND) |
3 | PACK- (GND) |
4 | PACK+ (12.92V) |
5 | PACK+ (12.92V) |
6 | PACK+ (12.92V) |
7 | PACK+ (12.92V) |
8 | PACK- (GND) |
9 | PACK- (GND) |
10 | TXD (UART transmit) |
As well as the meaning of all the pads on the back (not all board have these pads labelled - mine for example does not).

The SCL and SDA are especially useful - needed to reset the permeant failure flag using GitHub - o-gs/dji-firmware-tools: Tools for handling firmwares of DJI products, with focus on quadcopters.