There are BL-5J battery chargers on fleabay for about $2 with free delivery every N900 owner should have this in their emergency stuff for if you overdraw your battery.
I think there are some Pali charging scripts here on TMO to set the auto shutdown to a few % above the unchargeable state, maybe that would be a good thing for CSSU.
In an emergency while traveling I chopped off a USB mouse cable and gave my battery ten minutes with the red wire on + and the black on -. I risked popping the battery but it ended up working, I also did this once with an OpenMoko battery. Improvised 'jump starting' a battery is NOT recommended.