They will know your charging patterns. In the end, you have to trust the manufacturer or not connect a device at all. After all, they COULD use your Juicebox as a gateway to your whole network if they were so inclined. Of course, your Chromecast, router or net enabled toaster could do the same. You either live in fear or you don't.
2014 Rav4 EV, Blizzard Pearl White
2011 LEAF SL w/QC, Blue Ocean, returned at end of lease