I have a CCS, owned it for almost a year now. No issues with mine. Remember more "problems" will appear on web forums and make it seem like the product is bad. Its the nature of the beast!
I'm still only about 900 miles on my stock tires and have a long way to go. My commute never sees wet pavement, or rarely. I'll probably go with the conti's or the Kenda's again. I've only had one flat with the Kenda's (A small piece of metal) Otherwise they have been performing well.
On my commute today, with an intense headwind (one way) and temperatures close to 36 degrees. I went from 55.6 V to 48.2V biking 26 miles. Much more than usual, but about what was expecting given the conditions.
I have a 52V, the 21 aH battery they used to sell. It is wider than the downtube, but it connects to the terminal the same way the smaller batteries do. Its roughly (off of my memory) 0.5" wider.
Yes, I use this bag:
https://www.amazon.com/Topeak-Trunk-Bicycle-Molded-Panels/dp/B000ZKES0S/ref=sr_1_4?ie=UTF8&qid=1536708923&sr=8-4&keywords=bike+bag+topeak
With the panniers, they attached on the bottom of the rack close to where its attached to the frames.