BTC is a M5 base that allows you sit your M5 core instead of laying them down or hang on the wall. BTC is not just a sit for holding the M5 core but also comes with serveral features like temperature and humiluty detection(by SHT30), and charging base.
Although M5Core BASIC or GRAY can be attached to this base, but BTC can not charge them. Actually, our Cores, as we know, are built in chargin chip (IP5306). After plugged a USB cable in, the Core was charging without any charger.
Once M5Core has been attached to BTC, it can not controll ENV Unit at this time. Because BTC has been built in SHT30 sensor which will cause IIC address conflict.