M5GO BOTTOM is apparently the bottom part of M5GO which is a upgrade of basic bottoms, with a larger battery(500mAh),Analog Microphone, LED Bar , two more HY2.0 PORT(PORT B/PORT C),and more. Its back is compatible with Lego holes, and the pogo pin can be used to connect to supported I2C devices (such as BALA) or magnetic charging bases.