It sounds like they are making exceptions for the "usual suspects" with lithium batteries, i.e. cell phones, laptops, and cameras. It sounds like they are perfectly willing for "normal" devices to be excluded from the ban and probably they just haven't thought about the number of medical devices that also use one or they would have mentioned that too. Might be worth some kind of call or write-in campaign to get them to acknowledge a medical exception as well in the official literature. Could point out that surely they don't want literally every person with e.g. an insulin pump, BG meter, pacemaker, etc. to be calling them for exceptions or worse, to be cancelling their tickets assuming they can't fly, do they?