I don't understand this business about "low self-discharge" NiMH
batteries,
as I'ven never noticed any particular problem with them.

You've been lucky. I deal with a lot of 2-way radio handhelds that sit
idle for months at a time. The early NiMH batteries would self-drain to
unuseability in less that a month. At work, we replaced them all (at
least the ones we could find) after a year with newer technology NiMH
batteries like the Eneloops and such.

But why would you expect _any_ rechargeable battery (regardless of
chemistry) to keep its charge for several months?