I've found that:
Battery usage on OOS 13 (F.13) is slightly better than on OOS 12 (C.36), but nowhere as good as on OOS 11 (11.0.8.13). Admittedly, the battery was new on 11 and I've used the phone heavily for the past 18 months.
Charging speed on OOS 13 is better than OOS 12, but not as good as OOS 11.
See attached screenshots.
Notes on charging:
- 'ebay' refers to a 3rd party charger; '1+' refers to the OnePlus charger that came with the phone
- the charging times have been standardized so that 100% is reached at 1:00:00, making the graphs comparable.
Keep in mind that battery usage reflects the way I have my phone set up and my usage pattern. So don't expect to get the same results.