If it died from (less than, as not fully charged) 35v, i'd be very disappointed, as the website for the Ragebridge 2, in the first paragraph, advertises its ultra-wide 8-40v input very proudly. Which you're apparently now telling me is far from the case.

Even assuming that the LiPo was fully charged (both of them), 4.25 x 4, then doubled to account for both, 34v. Except they weren't fully charged anyway, so would probably be at least 2-3 volts shy of the above math.