I already did some stuff with ESP8266 and for a new DIY project I'm looking your ESP8266-EVB-BAT product. I've downloaded the schematic, there is a point I can't understand from my previous experience, why GPIO15 is connect to 3.3V via a 47K resistor. I always thought that this pin should be grounded for boot from flash or UART.
Thanks in advance.
It is already grounded in the design of the small board, that has own schematic here: https://github.com/OLIMEX/ESP8266/blob/master/HARDWARE/MOD-WIFI-ESP8266-DEV/MOD-WIFI-ESP8266-DEV_schematic.pdf
GPIO15 is pulled up mainly to ensure compatibility of ESP8266-EVB-BAT with our extension UEXT modules (sensors and so on). In the UEXT connector GPIO15 acts as chip select for the SPI and it is recommended to have an external pull-up.