My 44,4 V, 27 Ah (=1200 Wh) pack weighs around 6,0 kg, too. In total my backpack (Deuter Attack 20) weighs around 10 kg, including water, some tools etc.. I don't have any problems with this load at all, even today when I rode 2:40 h on more or less rough singletrails. I would never think of...