A couple of these will work on/off grid, should you find yourself in a place with no hookups.
https://www.samsclub.com/p/marine-27magm-18-mo-free/prod21234614?Not too pricey, and AGMs are set 'em, and forget 'em. Good in hot/cold and maintenance free. Good total amp hour rate, not T105 good, but good for a night or two off shore power. No idea what your charger looks like, so get a good one, if it's an old single stage, and you'll be good to go.
Take care of that medical issue first, though. Batteries can wait.
Best wishes, and good luck with both.
