NimH batteries tend to weigh less than NiCd. use a digital scale to
weigh your existing pack. Go to a shop and take the scale with you.
Weigh a couple of AA Nimh. You should be able to tell the difference.

NimH are not neccessarily better or worse than NiCd. They are just
different. Different battery chemistries suit different applictions.

have a look at this link for some answers

http://www.starbatteries.com/battery...imh%20superior

I think NimH can self discharge quicker than NiCd. About 1% or 2% a day.