I got spoiled by the fantastic battery life of the SR25, a legit 20 hours, so for me the RS6 is decidedly underwhelming in this department. However, I'm willing to forgive this as a trade-off for the SQ improvement on all my IEMs, especially the Z1R and Andro2020.
I don't us a DAP all that frequently, so far with the RS6 I pretty much always top it up after about 1-2 hours of use. I can't say for sure how long it would last from 100% down to 0, but I think I'd be lucky to get 4-5 hours max.
I think I read somewhere that Flight Mode is a good way to conserve a bit of battery, but then you are limiting yourself to local files. Any other tweaks/recommendations are welcome here as well, thanks!!