Hi ruby2 and welcome
!
I've been puzzling over your predicament since I read your post yesterday and and I wonder whether this an ideal application for the use of a fuel cell. I know nothing and have no experience of the medical condition but reading the 'blurb' about an
Efoy Fuel Cell it occurred to me that it might do the job.
Its not a cheap option but I imagine that reliability is the main consideration and although I can't offer a definite solution it may give you something to research and ask a lot of questions to the manufacturer/supplier.
Hope this helps.