645 question ...

[Godfrey DiGiorgi]

A very kind individual has loaned me the use of a Pentax 645 for a  
while. It just arrived today ... a nice beastie. I don't have time to  
do much with it this week, most likely, but definitely need to get  
some batteries.

I know it takes six AAs: NiCad, Alkaline and Manganese are listed in  
the instruction manual. Any idea whether NiMH rechargeables or  
Lithium disposables would be safe?

thanks
Godfrey