The HP-94 is an industrial computer which was never released to the public. It was intended for companies which were supposed to develop custom software for it. Unfortunately it was too little too late probably because the calculator never actually reached the users. Few were sold to developers and therefore the machine is quite rare.
An excellent description is here: HP-94 at MofHPC;
The calculator came in 3 different versions: 94D, E or F. The D version (presented here) had only 64Kb of memory, the E and F versions had 128 and 256K respectively.
The following are images of the HP-94D which is in my collection.
The batteries are of course dead. The calculator has a charger which is rated for 6V; I therefore assumed the battery will be 4.8V to 6V and I seem to have been right, the calculator works well when powered with 5 to 6VDC on the battery terminals. The polarity is like in the image below:
