M5GO BOTTOM is apparently the bottom part of M5GO which is a upgrade of basic bottoms, with a larger battery(500mAh), LOGO-compatilble holes, Analog Micphone, LED Bar , two more CONNEXT PORT，and more.
M5GO BOTTOM is the same Bottom of M5GO Lite, M5GO IoT Kit and M5Fire.
The unit arrived and works. I'm a little upset that the original unit only lasted 3 months
Has to go with the M5GO big battery bottom. Very useful as you can keep the charging base permanently plugged in and stick (it has magnets) the unit on when it needs charging. There is a bright LED to indicate charging/finished.