It's been a little while since I've paid attention to battery
Sennheiser says something like "up to 31 hours", but I believe their literature also says expect around 20 hours real-world.
In my experience so far I'd say that's about correct. I commented a few times fairly recently in the thread about disposable vs rechargeable batteries. There I was commenting about fresh events and so numbers were a little more accurate and real. The way I remember it, I'm getting somewhere around about 15 hours before the low battery warning sounds. Extrapolating from that percentage state of charge, the 20 hour number works out to be about right. That's not enough in my opinion, to say that rechargeable aids are ready for the real world, but it is enough to more or less "get through a day". My experience was based on what I would consider light streaming and easy use. Mostly quiet all day, a phone call or two, and maybe streaming a podcast. Certainly not heavy use, or even moderate use for an active person. My days are long though, aids powered up around 5:30 or 6:00 AM and off generally around 10 or sometimes 11 and I wear them all day.
I've found that on days when I do for example some yard work in the middle of the day, then drop the aids in the charger while I shower.... or even better when I let them charge while I mow... then I end my day with enough margin for it to be comfortable. Not enough to get through the next day, but it's good. Even just a 10-20 minute top-up seems to help quite a bit.