Do you mean 'internal resistance'?, if so it's very low, but I've no idea what value it might be, and it will vary with the size and make of battery, plus how charged it is.
Why not look at a manufacturer's datasheet?
Also, if you look at their application notes and charging guide, you'll see about things you haven't thought about yet. Don't re-invent the wheel. :lol:
That's why it's VERY, VERY important NEVER to short out a NiMh or NiCd battery - they contain enough energy, and a low enough internal resistance, to destroy themselves.