I also have one of these, the medical type.
Someone on the UK forum sold a few a year or two back.
They are as mentioned a sealed unit, and are meant to be discarded when the batteries run flat, BUT, you can get round it and replace the batteries fairly easily.
If you use a sharp Stanley knife/craft knife, and gently make a cut around the plastic cylinder approx one inch from the battery end, you can replace them.
Once installed, hold the end cap tightly and put some electrical insulation tape around the cut section to keep it in place until the next time.
I did it myself in about ten minutes, you could use a fine tooth hacksaw if you prefer, just go gently.
These burners are far too good to bin, and you can get many more years out of them with this trick.
Either that, or start dating a nurse!!