As a person that is in the Audio Visual industry I'd look at where you
get your batteries from. Why? Well if you can buy them for some
rediculas low price then just keep buying the alkalines. It's just a
lot less fuss!!!

I say this based on the fact we use mainly 9 volters in about 6 radio
mikes on most gigs. We end up paying approx $1.50 per battery. For us
we know we can get 8 - 9 hours straight out of one alkaline battery.
As not many gigs go past this time you simply work on the fact that
each time you use a radio mike you put a fresh battery in.

See Nical Metal Hydride rechargables are the ones that don't develope
memory problems - but they are more expensive than the normal
Alkaline. They also "go flat" faster because they are still only 8.4
volts at best. So when you weigh it all up any rechargable and
especially the old Nic Cads when fully charged aren't really
delivering the volts the mike wants. Yes but it's only 20 cents of
electricy to recharge it up again! True! But it will still go flat
faster than the Alkaline as it is behind the eight ball from the
start. Then if you "kill" it by "over charging" or giving the old Nic
Cads "memory" then your economys are shot. Yes!

Seriously I'm sure the numbers work in the my favour if you do some
sums. Remember rechargables "loose their charge" if let sit too.
Factor that into your sums. You will see i'm right - a lot less fuss -
just get a big box of alkalines and keep feeding them in.