You'd be surprised what even a small PV-cell can do when no load (device shut off, battery full and cut out due to protective circuit kicked in) and you give it a flash from a photography electron flasher.

Estel is absolutely right with his concerns. I'd like to add concerns about USB2.0 electrical properties getting messed up by your rework, resulting in data errors or even complete failure to establish connections at highspeed (480Mb/s). Even some cheap USB cables can fail for highspeed when the building quality and cable are poor.

[edit] re your 2nd post: all that's reasonably hot-swappable in N900 is already made to support hotswap. uSD slot gets powered down when you remove the battery cover, so you don't destroy the uSD by removing it while powered. SIM is useless to hotswap anyway. So what's the rationale of your hotswap plans? I failed to get the point.

[edit2] With sufficient electronical expertise you could create a convenient way to hotswap the battery, but the needed know-how is not trivial. To give you a starter: you MUST NOT parallel-connect two LiIon cells with differing charging level.

/j