are mAh for batteries relevant?

Hi guys,

I was wondering if the mAh on an battery pack is important or relevant, so you recognize a difference?
I've read a lot about "Nerf voltage mods" where modder change the standard 3xAA nimh batteries (1,2v each = 3,6V) against 2 Li-ion batteries (3,7v each = 7,2v) and one "dummy" battery for better perfomance and range.

Now I'm also thinking about changing to Li-Ion (with around 1500mAh) or just buying better/stronger nimh batteries with around 2500mAh.


PS: if this topic does not fit, please remove it from this forum