These 9V USB-C charging batteries do not fit in the A9 (too large). NOT a complaint against the A9, just wanted others to be aware so they don’t waste money on something that won’t work in their device.
Had hope since the regular MaximalPower 9V do fit.
I can’t speak to A9, but I describe my experiences with 9V lithium rechargeable batteries for the P9 prototype here:
I learned to get rechargeable lithium 9v batteries without integrated charging (9vs with integrated charge controllers are the ones where you can plug micro-usb into the battery directly to charge it).