WWE updated their Key Performance Indicators on Tuesday. In them, they reveal buyrate estimates for WWE Battleground and WWE Hell in a Cell.
The two pay-per-views drew an estimated 363,000 buys combined. How that averages out, I'm not exactly sure but I can tell you that WWE Battleground was one of the lowest bought pay-per-views since WWE Over the Limit 2011, which drew 140,000 buys. Hell in a Cell was up slightly from last year, which drew 199,000 buys.
You can evaluate WWE's Key Performance Indicators at this link.