The LR50(PX1A) can replace the the now banned MR50 (PX1) which was a 1.35v Mercury Cell. Although higher voltage than the original from many years ago, most things cope well with the up-voltage. Currently this is the only replacement battery for the application, there is a voltage dropper system in the market place, but these are very expensive and hard to find. Picture shows the actual item, sold.
eBay