Certain batteries/cells are either nowadays virtually impossible to obtain, or can be obtained (usually from online sources) but are rather expensive. It may therefore be useful to know that certain of these can be found inside more easily available (and cheaper) batteries, hence we're putting this thread together.
The first example is the now all-but-forgotten Ever Ready U10 1.5V cell:
If your ever stuck for these you can get them cheap, simply hack a 1289 (3R12) battery and three are found inside wired in series but make sure you insulate them before use by wrapping a paper jacket around the cells. I am sure some test equipment uses these, it's cheaper than buying them as one of these 3R12s cost around £2.
Here is a picture of an Ever Ready U10.