@Ken
I would guess all batts down (but unlikely even yoi did not take care of them ). As chance both N900s broke is there but even more unlikely. Did you store your spare with battery inside? (high chance of drained, too).

I would try a full ppwer cycle before/after charging (shut down, batt out, push power button a few (10) seconds, batt in, boot) but as said I guess batteries drained (even your description in OP would tell me everything good ).

Best chance get an external charger (a 5800 or something cheap chinese universal like YIBOYLIAN AD-04) and try again after charging outside. Or just get a fourth one to check (not preferred)?
Or even better check capacity of batteries (simply voltage after charge and after startup try/tries).