Just saw this one from Thule.
It has a dedicated area for your extra battery, but to be honest, I am not sure it would hold the newer "integrated in the downtube" batteries a lot of us have.
Finally pulled the trigger on an Osprey Raptor 14. It only took me 6 months to decide, but was not a priority.
Was going to get it's maiden voyage yesterday but we got "Smoked Out" and will reschedule. Goat Creek Trail from Canmore to Banff - looking forward to it.
Will be riding with @Prairie Dog his BIL and one of his other riding buddies from Red Deer (and perhaps +1).
I have used the pack quite a bit and am very pleased with it overall. Only real downside is there are so many places to put things, it's hard to find the stuff you want from time to time.
For Canadian riders who are looking for similar products, MEC has the Gregory Endo15 for 21% off for the next few days c/w free shipping.
We don't see the higher end stuff like Osprey or Gregory on sale very often around here.