https://www.rba.gov.au/publications/bulletin/2020/sep/retail-central-bank-digital-currency-design-considerations-rationales-and-implications.html
Reserve Bank of Australia 17th Sept. 2020
Decisions regarding in-person, online and offline usability
If a retail CBDC was being designed as a replacement for physical cash then, at a minimum, it would need to facilitate in-person payments – for example between two individuals or from an individual to a merchant in the retail environment. But, being an electronic system, it would presumably be possible to design it so that the CBDC could also be used to make remote (or online) payments. In this way it would function in much the same way as cards currently do.
As a form of electronic payment system, CBDC might be constrained by the availability of electricity and telecommunications systems, in contrast to physical cash which is ‘always on’ for exchange purposes. However, as noted above, it may be possible to design a CBDC system in such a way that it could be used (at least temporarily) in an ‘offline’ mode, which would be useful in remote locations and offer resilience benefits when power and telecommunications networks were down. For example, it might be possible for CBDC stored on a mobile device or some other small, battery-powered user-access device to be securely transferred to another device via wireless technologies even in the absence of power and telecommunications. However, there would still be a periodic need for power and network connectivity to reload or redeem CBDC balances against commercial bank deposits (and to recharge any batteries). As noted above, an offline mode might be easier to implement with a token-based system than an account-based system.