It depends on your oxygen needs, liters per minute. If it's pretty moderate -- like under 4 or so -- then you may be able to get by on a portable oxygen generator like the Inogen One, whose batteries can be charged by either 120 or 12 volts. If your needs are higher, it gets harder. Our Inogen has a max of 6, and that's with oxygen pulse, not constant flow. And it is somewhat marginal for her at 5000 feet.
As others have pointed out, you always want to carry a backup supply. We carry some extra larger bottles with a regulator just in case. (And, indeed, the Inogen's 120 volt power supply kicked the bucket a couple of weeks ago, and we needed the backup.)
:)
Lynn