I use my WS-50 at an open mic night - plug it in and switch it on about 8:15pm and turn it off about 11pm. I've also used it for various gigs where it's switched on for 3 hours or so, and used to use it in rehearsals with one band where I'd use it for two 3-hour rehearsals on one charge. Looking at the Amazon specs, the WS-50 was released in 2019 and the WS-90 in 2022. Mind you, the WS-90 still has micro USB on it which is a slight annoyance with the WS-50, especially as the MS-1 IEM wireless is USB-C so they can obviously do it if they try. I suspect that the shorter range and the longer battery life are related. The WS-90 does have four switchable channels which would be useful if more than one band member was using them, and possibly would be useful if there was interference on one channel.