A small silcon diode, like 1N4148 would work fine, but a Germanium diode will allow you to squeeze more life out of a 3V battery, by dropping less voltage.?
If the battery is in a clip, it's less important than it was originally, but Germanium diodes are not anything particularly exotic, so get one of those, yes.
FWIW, I've bought 1N34A Germanium diodes on ebay - I got 20 for ?1, though they took a while to arrive, so you'd probably want to shop closer to home.
To check a diode is a germanium one (Ge), use a meter that has a diode test or put it in series with a 1k resistor and use a 9V battery, then measure across it.? In either case, it should show close to 0.3V.
- Andy
AndyHornBlower