Hi there,
Well I see several free ways to approach this problem. One solution would be, Xiao to Xiao over BLE.
one central one peripheral with the idea that more peripherals could be added later like pedals and displays , etc.
AFAIK, system on sleep power consumption is uA. your battery should easily last that long.
a second solution is a RF-Trans/Reciever to a Xiao would be receive only but still manage low power on the Xiao side.
The first is the best IMO. BLE to BLE opens up a whole network of possibilities. You could do CAN-BUS between peripherals and have one Xiao filter and control all the messages and BLE to a phone for Data and control.
lots of possibilities.
HTH
GL 
PJ
you can use the online battery calculator, digi-key has one. put in your numbers and see about how much burn you have given the battery size and run time. 