Why is one battery marked #1 on the Voyagers?

[jebem]

To replace the three battery cells on the original Voyager HP calculators while minimizing the risk of memory loss, the job should done as swift a possible, despite the fact that memory retention on this electronics is huge and there is no need to hurry.
To be fast it must be easy too.

On original Voyagers there is a #1 marked in one of the batteries in the information label.
Also these initial machines didn't use the spring coil contact or plastic retainers as the later series. Check it here.

This is the procedure I use to replace the batteries on one of my 1982 HP-15C Voyager calculators:

While holding the machine on your hand at a 45 degrees inclination and having the battery compartment in the upper position:




Drop the first battery cell in lowest position (#1):



Drop the second battery cell in the middle position:



Drop the the third and last battery cell on top.
Job done.



If you are not able to insert the third battery, check the batteries polarity orientation.
The negative side (smaller area) must be facing down.
In this example I tried to insert the three cells with the wrong orientation. They don't fit: