TL;DR: Expect 5-6 hours for regular use or maybe 7 hours if you listen at lowest volumes with the UTWS5.

Btw, a few days ago they added PEQ and multipoint with the UTWS5 now, see here for more info: https://www.reddit.com/r/headphones/comments/10x4o41/fiio_utws5_bluetooth_tws_adapter_for_iems_and/

There's also the UTWS15 (UTWS5 3rd version with ergonomics/etc. changes) or something like that, it may have better battery life, it's releasing probably this October 2023 or November 11.11 sale time.

I have multiple versions of the UTWS5 (and UTWS3) from the first batch (release in China/AliExpress/etc.), second batch, and so on.

Battery life is still somehow good. I basically use them every day, though that's not exactly true as I take breaks. Sometimes I go weeks/months without using the UTWS5 and just use my speakers/etc. instead.

Anyway, basically I use the UTWS3/5 for their full charge and rarely remove them from my ears or power them off. So for me it's continuous/nonstop usage, but other people will often put the TWS adapters or TWS earbuds back in the case when they're not using it.

In my case/testing/experience/et cetera at lowest volumes (2/32 or so volume on FiiO Control app) possible it goes like this:

UTWS5 + single dynamic driver/hybrids/tribrids/multidriver IEMs + regular AptX = 7 hours or so of battery life

UTWS5 + single dynamic driver and general hybrids/tribrids/multidriver IEMs + regular AptX Adaptive = maybe 6 hours and 30 minutes

UTWS5 + planar IEMs/some hybrid/multidriver/etc. IEMs + regular AptX (and AptX Adaptive) = variable, it's likely not gonna reach 7 hours for sure as you'll want more volume to hear approximately the same levels as a regular dynamic/etc. driver IEM. Personally clicking once or twice from 0 or lowest volume possible is enough to get the planar IEMs to be louder volume.

For context with my AptX Adaptive USB transmitter dongles like KB9P, I turn up the volume there first, like with planar IEMs it gets close to 100/100 dongle (Windows volume slider) volume, while still being at 2/32 volume on the FiiO Control app. That's mainly for everything at 100% or so with things like foobar2000, Winamp, MusicBee, VLC, et cetera. Or video games/etc. sound.

Then with some tracks or albums that are so low, I do have to press once or twice to get better volume and so on. Or if I'm listening to ASMR on Youtube, some videos are so low volume with planar IEMs that I have to click the physical buttons a few more times.

Here's some videos/channels for ASMR triggers: https://www.reddit.com/r/headphones/comments/xqq9kw/can_a_normal_person_hear_binaural_sound_when/iqcayk9/

ASMR Bakery's latest video, she usually doesn't do 1st person POVs (more just regular trigger assortment/variety/etc.), check her other videos: https://www.youtube.com/watch?v=3c4Zay0e1PU

Anyway, I listen at whatever volume is at that 2/32 volume on the FiiO Control app (it depends on the IEM), and it rarely changes unless I'm using a planar IEM or some IEM like the QKZ x HBB Khan which needs a bit more volume than other more regular IEMs too. Again, usually it's just 1 or 2 presses on the right side of the UTWS5 and it should be loud enough again.

I listen at that 2/32 volume as I legit never take the UTWS5 off unless I have to eat, use the toilet, et cetera. Sometimes I don't actually play sounds or ASMR and so it's just idle and that still drains the battery. But with Bluetooth devices the constant recharging is what kills the battery life, apparently, and so I just leave it on and so far it's working just fine. Other people report worse battery life now though.

Like others are saying they get the advertised 8 hours and that's not true, lol.

Most of these TWS adapters and TWS earbuds advertise that specific 8 hours of battery life but in practice it's more like 6-7 hours for people like me that listen at lower volumes.

You have to specifically look for TWS earbuds that have that long (8-10+) battery life, and for TWS adapters it doesn't really exist. There's those neckband adapters like FiiO LC-BT2 that have bigger batteries and should theoretically have better battery life, but again it depends on your usage (volume levels).

For people that listen at 50% or so volume and regular AptX, some of them get 5-6 hours with the TWS earbuds (and TWS adapters). It's a noticeable battery drain once you leave the lowest volumes possible. But barely any people will experience the change as it seems people only use these Bluetooth stuff for a few hours at a time (which is better for your hearing health, always take breaks and listen at lowest volumes possible).

This is just for additional context, but FiiO also has its new FW5 TWS earbuds, which is like the UTWS5 internals but with actual TWS earbuds stuff (no ANC though).

More info on the FW5 in relation to the UTWS5/future UTWS7/etc. and LC3, like Bluetooth latency stuff: https://www.reddit.com/r/HeadphoneAdvice/comments/z5pfj4/tws_iem_conversion_thingies/j2ps3qy/

Here's more info on TWS adapters like the FiiO UTWS3/5, KZ AZ09 Pro, etc. alongside adapters/converters, AptX Adaptive dongles (KB9P, YET-T10P, etc.), and so on needed for them: https://www.reddit.com/r/HeadphoneAdvice/comments/10hfuxn/wireless_earbuds_for_gaming_with_plugin_to/j58i33j/

Make sure you get the MMCX version of the UTWS3/5, here's more info about why (it's mainly due to IEMs that have recessed 2-pin ports, like the popular Moondrop lineup, etc.): https://www.reddit.com/r/HeadphoneAdvice/comments/v3hs92/iems_help_need_a_new_pair/iaz200a/

If you're using the UTWS3 outside with your phone, you should be good, otherwise for PC, there could be connection issues.

Here's a bit of context on Bluetooth pairing/connection/battery drain issues with the UTWS3/5: https://www.reddit.com/r/headphones/comments/vjwq2p/never_thought_my_endgame_would_be_wireless_glad_i/idn2t9u/

Here's more (direct) updated info about the AptX Adaptive USB transmitter dongles (KB8P, KB9P, YET-T10P): https://www.reddit.com/r/headphones/comments/zr41fe/which_lossy_codec_to_use_compress_with_before/j12cdwt/

For TWS earbuds, see here for more info: https://www.reddit.com/r/HeadphoneAdvice/comments/10hdr2p/are_there_any_wireless_earbuds_witouth/j58keli/ and https://www.reddit.com/r/headphones/comments/10kai7u/should_i_keep_ear_buds_out_of_the_case_after/j5so87z/