Can you elaborate on your technique a little (equipment used, exposure times etc.)?
Canon 20D, Canon 10-22 @ 10mm, f 4.0, 25 sec., ISO 400, sometimes ISO 800.
good tripod (I use Manfrotto 755B)
Timer Canon TC-80N3 (now I can't imagine taking photos without this gadget)
Make sure that you always have few fresh accumulators in pockets,
in low temperatures...
Few days ago I made simple voltage regulator for external
12V accumulator, with long wire (I have no battery grip).
After first tests, with 12V/4000mAh accu, it allows 22 hours
of shooting in -10 degrees C
(of course timer did it, not me )
And I wish you good luck and bright northern lights