That’s what I did also, name brand adaptor & 2 - 2 AH 20V, good to hear that the 2 AH Li-ions are lasting longer than the Ni-Cads did.
The old style 18V Chinese aftermarket battery was cheap enough to take a chance on, so I thought I would give it a try, it is supposed to be rated 5 AH. We will see how that one turns out.