You will never get that battery if it makes the device thicker. I was in the industry, we made smartphones with a two day battery. Full on thick, in direct response to customers asking.
None sold. Period. It was something like 8-10mm thicker.
Everyone looked at the one with the thick battery then the thin and bought that.
Motorola makes phones with two day batteries (5000 mAh standard, some going up to 6000 mAh) and their market share is growing, recently reaching third place in the US behind Apple and Samsung. And it’s all in the standard size, forget being 8-10mm thicker, they’re 8-10mm total.
Purism made the Librem 5. It’s a chonker and has bad battery life and they only sold a few thousand units. However, if rappers can make dumb phones and sell out 10k units in a few days, I dare say there’s a market for thick phones with good batteries, it’s just that rappers and celebs do better marketing and have a wider audience.