For other batteries ideas, there were some builds that used coin cells as batteries. For example this one: https://www.reddit.com/r/ErgoMechKeyboards/comments/11piaav/lütt_un_lütt_coin_cell_powered_bluetooth_split/?utm_source=share&utm_medium=android_app&utm_name=androidcss&utm_term=1&utm_content=1
For other batteries ideas, there were some builds that used coin cells as batteries. For example this one: https://www.reddit.com/r/ErgoMechKeyboards/comments/11piaav/lütt_un_lütt_coin_cell_powered_bluetooth_split/?utm_source=share&utm_medium=android_app&utm_name=androidcss&utm_term=1&utm_content=1