What size Battery do you use?

I am a hardware developer working on a new wireless module targeted at ergo splits. I am currently designing the battery circuitry and I would like to know:

(1) What size battery do you use (e.g. in mAh)?

(2) How long does it take to charge and does charge time matter to you?

(3) Which do you prefer:

—> small size/light weight at the expense of battery life? or

—> long battery life at the expense of size/weight?

(4) With the above in mind, would you prefer a battery that is larger, smaller, or the same as what you have (in terms of capacity and dimensions)?

Any other thoughts/comments on the topic are welcome :)