XXL Battery case enlargement 25 mm.
Extra large enclosure cap to power your ESP8266 or Arduino with 3x AAA battery.
The original case depth has only 5 mm and this version extend to 25 mm.
https://www.adafruit.com/product/727
Amazon.de - Batteriehalter-AAA-Batterie-Aus-Schalter-2-Pin-JST-Stecker
aliexpress.com: 3x AAA Battery Storage Cover Box with ON-OFF Switch