In case anyone is interested, Kogan currently has 4 x NiMH 4000 mAH C cells as are used in the SDC for $15 with free postage.
Perhaps they want to get out of this item.
I paid them $39 last year for the same batteries, plus postage. I can attest they work for at least 5 hrs . Probably more..
Now might be a good time to stock up.