The Question is:
In a VAX 4000-400 CPU, is there a battery that keeps the clock running when
power is absent from the CPU? If there is one, can it be replaced with the CPU
The Answer is :
Yes, there is (clearly) a battery.
Depending on the implementation of the particular VAX processor module,
the typical VAX system used a NiCd battery pack or used a DIP chip
("Dallas" watch chip) with an integrated battery -- most (all?) members
of the VAX 4000 (Q-bus-based) series systems usually used a 3.6V NiCd
battery pack, and Q-bus-based systems typically had the battery mounted
on the module bulkhead or operator control panel.
The OpenVMS Wizard would not encourage you to manipulate the internal
system electronics within the system enclosure with the system power on.
Please contact your hardware service organization for assistance.