A) Cable =
"MOST DATA" =
B) Non-Cable =
Hesitatingly, I finally asked in a Google Fi support ticket and that is the response I had to wrestle from the reps (who did not want to use the word "Cable" specifically, and in their wisdom specifically avoided the word).
Their support documentation does not use the same language as their User Interface, leading to misleading directions and ideas about what it means. (I gathered that some of the front-line support representatives did not know about the "cable" part from reading their own documentation pages they copy/pasted me as responses, before I finally got a clear answer. Meaning a random user who does not have the greater technical literacy, would be at their whim. That is not acceptable User Data Policy, for an adult company writing documentation, to not catch that glaring lack of clear language, and should have been noticed long before I had to formalize this report.)
On an official documentation/inteface-level that is appallingly not warning users of the SEVERITY of not using a cable transfer, saying "most" is definitely not clear/mature enough for a final warning message. (If you heard or thought that not using a cable would work to keep data that is not in the cloud, multiple Google representatives also thought so it seems, and I am thinking about the rules for proving the whole email support ticket, because there is a disconnect if connecting user's devices (especially when internally between Google the same provider) is not treated as important as enterprise data retention policies, why do companies get 100% guarantees but I get just a a cable warning, we're going on the sixth generation of Google Pixels and there need to be user-specific standards for once.)
It is already appalling that GPixel is not designed with removeable batteries (and we break our warranty if broken and repaired), and egregious to add insult to injury by making Battery Sharing the only way, to save your life's data. Can you imagine the abuse of an enterprise being told they need to use a terrible battery/cable or else?
There is not a technical reason for this that is not opinionated infosec policy (a policy that is not codified or codifiable into law, because it's stupifying opinionated conjecture [the idea you Users need a unreliable error-prone asking-for-problems "Battery Sharing" cable, and can not be trusted with the ancient litany of other great official trusted methods known to transfer data well and reliably just fine instead like Bluetooth and Wifi too] written as a wise/official-sounding User Interface security warning dialog as-if it is just "good advice" for a user who needs dumbed-down 1-sentence language yet is given a 100-page Terms of Service policy? Users paid your bills too, hello. My data is more important than saving face that "Battery Sharing" was a good idea for primary backup), thus unlike enterprise Data Retention policies which would GUARANTEE a connection and archival (and say Hello politely in every email personally and not using canned responses, for an enterprise superuser customer), we users are not given full information standards, our US congressional law does not speak the same language as coders, and thus users are forced by this to go through hoops.
In the Warning Dialog, We might as well write 'Fix with a new battery, or sacrifice your data', to save someone's life's data, which should be the point if not a corresponding documentation law, the User's Data should be sacrosanct.
If during setup "Battery Sharing" is not working, you must fix your battery first at all costs because there is not an alternative option, or your data will not survive, (Raw ROM copying is not a user-friendly alternative option, & Google could do much better realistically, it's not the user's fault if there are not full backup redundancies built-in, why are we forcing the only one option that may be physically challenging) so please make sure to do a full cable-only transfer to be complete.