NiHaoMike, reply #40:
You can get multi-cell NiMH chargers for stacks of series cells. You can then have a wire which plugs in to a device to let such a chrarger be connected. Cell removal only happens when cells are worn out and old, that is when having the standard form factor helps, you can take them out and get new NiMH AAs to fit in their place. If you want a device to "last forever" you're better of focusing on easy replacement of parts with generically available spares, rather than attempting to have things which never wear out. Charging could also be done entirely with onboard circuitry, you'd use a wire, or an inductive coil system to simply supply 5V or 12V constant voltage, and inside the device the charger would convert this to the mroe specialised requirements of actually charging the cells. Again, cells would only come out individually if/when they wore out, for charging they'd remain inside and in series.