My initial review:
Finally made up my mind to get that heavy battery off the rear rack and did the research which led me here. Battery is LiPo 48v 20AH. 70 x 170 x 255 mm (2.8 x 6.7 x 10 inches), 13 lbs
I emailed the seller 6/5 (Elisa in this case) and told them I needed the bag pronto since I have a trip coming up. Email returned within hours, no problem, we will priority mail immediately, please send gift via PayPal - $65 total. Ok, I am happy so far and sent $$ immediately.
6/8 Bag arrived - envelope seemed small, I was worried it wasn't going to work for my rectangular shaped pack. WRONG!
This pack is everything I had hoped for so far. Pack has giant wide straps of velcro all around, 9 in total. 2 slits for wire ingress/egress, one front edge and one rear. Headlight routes in through the front, battery routes out the back to controller which still lives on the rack in that frumpy chinabag (for now). The slits easily accommodate an Anderson powerpole connector and seem to cinch closed around the cables quite nicely.
Per the previous advice in this thread, I have it mounted so that the bottom of the battery is on a layer of shipping foam cut to cradle around the bottom of the battery, and rests against the frame. The width of my battery (18650 based, single layer) fit perfectly into the designed width of this bag. 7" across the short side fit PERFECTLY in the bottom edge of the bag, standing on end, oriented as seen in the picture below. That is a second battery in front of bike for scale, but there is one IN the bag too. Hell, I could almost get another battery in there if I wanted to, this thing is huge. I like that, as it takes almost full advantage of my 22.5" frame and I carry plenty of stuff with me.
Boy, am I glad I moved this battery to the triangle! The balance of the bike has been restored, and my bike behaves like a bike again. My "death wobble" when I take my hands of the handlebars at any speed over 10 mph has gone away too! I didn't realize how I was fighting it into turns, leaning on the front tire to keep it down, and compensating for the top heavy-ness of the whole mess. My ride in tonight was just..smoother and more enjoyable overall due to the weight distribution change. I can't recommend moving your battery forward enough at this point. Hopefully my rear rack will hold up better now under a more reasonable load of beer and chargers.
I will update this post as my experience continues with the bag. Off to Yellowstone I go!