Is the iFixit replacement battery for the DS Lite the proper mAh?

I was doing some research into replacing my DS Lite’s ancient battery as it barely holds any life anymore (an hour at best) & I cannot tell if it is swollen under the deadly grip of my childhood NERF case on it (I will take precautions in removing it, don’t worry). However, I couldn’t help but notice that the original battery is 1000 mAh, but the iFixit equivalent is only 850 mAh.

Is there a distinct difference between the mAh levels, and if so, could someone explain how? If not, is there still a risk of harming my device? As I do not wish to sacrifice my childhood DS Lite of course. Thanks for reading if you got this far.