My understanding is with the 2nd return you have increased the estimated battery life of both hearing aids and they both sound great. Sounds like success to me. I suspect there are lots of variables. I don’t know Resounds at all, but there are different demands placed on the different hearting aids? (I know with my KS9, the right side always dies first which I’ve attributed to the streaming going to the right side, as well as having a somewhat worse loss of hearing) It also sounds like you used different methodology to estimate the battery capacity (discharge 20% and multiple by 5 versus discharge to 10% and divide by 0.9) I also wouldn’t rule out lapses in quality control with supply chain issues. I also think the odds of something else failing (most likely a receiver) before you have battery issues is very high. The data you reported is definitely interesting though.