Wondering about the battery life of the 4GB RAM devterm

Been researching for quite a bit about handheld devices like these (I already bought the 4GB RAM devterm), while battery life isn’t my main priority, I’d like to know how much I can expect in hours before needing another charge, from batteries that add up to 10k mAh. I do not consider myself capable to just do some funky formula calculation to get an average, so I’d really like to know, please, and thanks for reading.

(I’ll probably just use it for JavaScript related development, and not necessarily having the browser open all the time I’m using it, to give an approximate idea of what to consider with the calculation of mAh usage and time)