So use a battery of a standard form factor and make it easy to replace. E.g. one AAA battery per device is easiest. Most coin-sized lithium batteries are also rechargeable, explicitly or implicitly.
What do you mean by implicitly? Last time I checked, most of button/coin-like batteries (CR2032 and the such) aren't know to be rechargeable, unless you specifically get rechargeable ones.
you don't seem to have really understood my points, because you aren't engaging with them; as it happens, you're also mistaken about coin-sized lithium batteries (though any battery can be slightly recharged)
