After looking at a technical service manual for an AX100, it's not totally clear if this has changed over the various different versions over the years, but there appears to be a battery access flap on the front edge of the till, just under the keypad. The batteries appear to be mounted in a holder that pulls out of this access flap.
Sorry, I'm unable to find any advice on Mac connectivity.
If the battery suggestion is correct or not, reply to this thread by using the 'add an answer' button which will help future users needing the same advice.
Rupert, April 2020
