Many devices use lithium-ion packaged batteries that are fairly close to the size of a Compact Flash card.
We propose a standard Lithium-ion 3.6V package that is an exact fit in the CF I or II form factor.
This would have many adavantages; batteries could be charged in any CF slot, be it in a desktop
or notebook pc, in a camera, or in an MP3 player, or via USB (with an adaptor).
The battery could be interrogated by the host to determine its health, via a standardised interface.
Batteries could be easily swapped between devices.
One spare charged battery would be sufficient for numerous diverse devices in an emergency.
On the downside, manufacturers would no longer be able to charge outrageous prices for cheap little secondary power cells just because they've got a "proprietary interface".