I do not think it is stupid and I think there are lot of users who feel the same as me.
I have Huawei p20 pro smartphone. Battery lasts for 2 days if I dont use it all that much.
Personally I would have chosen Huawei P20 pro plus with huge battery that can last for a week, if there were such a thing! I would gladly accept the increased thickness and weight... there are a lot of advantages I can think of:
1.) Right now I carry around 3 things: Smartphone, battery pack & ES100,
with big battery on Qudelix 6k, carrying around a battery pack is no more necassary, as Qudelix 6k could also function as battery pack if needed. Only 2 things to carry around!
2.) You state battery life of 21 hours on Qudelix 5k. It is going to be a high quality headphone amplifier also able to drive high ohm powerhungry headphones in balanced mode.
surely battery life on 5k for those is more like 9-10h - not all that much, I will have to think about loading it more often.
Having a big battery will allow for loading it one time, putting it in your pocket and use it for a whole week without having to think of loading the battery - very user friendly I think!
It is going to be a high quality audio device, and as such I would not mind if it was bigger...
3.)Not having to load the battery often will drastically enhance battery life in the long run. Battery on my ES100 is starting to go bad after 1 year. I really like it, and I hate that it is going to break at one point.
When I love something I dont want to have to throw it away after 2 years, I want to use it longer! With a new device, you always have to get used to it, which can be annoying... Also it is creating electronic waste.
Big battery would make a possible "qudelix 6k" more sustainable, as one could use it for many years.
Battery on qudelix 5k is improved by 60% so it is already better. But still there will be a lot of users wishing for more I think... I am definately one of them!
4.)For you engineers it would not be a lot of work, all the engineering has been done already for qudelix 5k. All you would need is another housing.
In the app you could apply a switch "use 6k in usb-dac mode" / " use 6k only in bluetooth mode and as battery pack"
If the device is qudelix 5k this option could be hidden in the app, as it could never serve as a battery pack.
5.)The ES100 is ridicoulusly small compared to my headphones (Meze classic 99).
I would not mind at all, if it was 5 times as big, then it would not feel like a tiny plastic toy, but like the serious hifi device it really is.
Me as a user, If I had the choice between bulkier qudelix 6k without clip and bigger battery and qudelix 5k being smaller, lighter and cheaper, I would always decide for qudelix 6k!
I wonder what other users think about it.
again: I am not asking to change spec of 5k - just giving you an idea for a qudelix 6k.