A simple query from a simpleton...

I have a cordless house phone, whose internal batteries are worn out.
They are feeble 700mAh NiCads who hold their charge for only a few
minutes' use now. Can I replace them with some 2100mAh Ni-MH's, of
which I have loads (Recommended charge 7H 420mA)? Or will they not
charge properly on the phone's base unit (Claimed output 9V 300mA)?
And if not, should I just replace them with exact equivalent NiCads?

Thanks in advance.