I do get around 40 miles until 20% on level one with my 12.8 which isn't bad at all. Level 1 and peddling at about 24 miles per hour.
For me with my gen 1 CC 24mph is level 3 with a good effort in ideal conditions. I'd love to upgrade to a CCS controller, but I'd need the higher capacity battery to go along with it. Only have the LED display & 12.8 battery; going by the bars I used 60% on calm days, 80% in headwind days, & 90%+ in winter all in sport mode.
I wonder if fatigue failure could be thing considering over 16k miles on the bike already so maybe a good idea to buy new anyway,