MZ-S and batteries

[Patrick Genovese]

I use an MZ-S plus battery grip an my only gripe with it it the battery 
consumption.

Are there any solutions ? mods etc..
How about NIMH batteries, I know the manual says you should'nt run it 
off rechargeable batteries.

Is that just coz of the lower voltage ?
or are there other repercussions ?
Tnx
Patrick