In the process of reviving a troubled N900, I ran into a dead end for a while by draining the battery entirely and not having an external charger.

Battery has been fully charged now using only the charging cable and the N900. I've found that it holds a charge if I unscrew and detach the screen while charging it.

Haven't determined whether this is preventing the boot loop or just not drawing as much power while boot looping but it's been enough to buy me some time to reflash. Might work for others in this situation too.