It's probably 600-900 meaning both or anywhere in between. I had a small ego one for my first one and it was 600-900mah. Now I have a medium sized vape pen battery that is 2200mah, and another small backup one a tad longer than this one that's 1100mah. The VOLTAGE is the small number, but the mah is the output strength used when "smoking" from it. :) hope that helps.
And the person that said "let's be real", does NOT know what they are talking about.