Powering a HP 67 without battery pack?

[Lode]

For powering a HP 67 without battery pack (and without willingness to use any batteries):

Question 1) I read in multiple threads that powering it with the HP DC adapter/charger can break the card reader. However, this one is already known to have a broken card reader. Is it safe to use in that case?
NOTE: I tried it *very briefly* and it worked, it turned on and could calculate.

Question 2) What is the +/- side of the battery terminals? The terminals in the photo in this thread (https://www.hpmuseum.org/cgi-sys/cgiwrap...ead=219662) are on the opposite side as in my case, in my case they are on the left (with the top of the calculator at the top of course). So are + and - reversed (+ up) in my case?

Questions 3) Is it safe to power it with an adjustable DC power supply to the battery contacts (once knowing what the + and - are)? should it be set to 3.75 V or to 4.5V? How much milliamperes is it expected to draw?
NOTE: a very quick experiment did not work, unlike the HP adapter afterwards.

Question 4) Is it safe to power it with USB (by modifying a USB cable first), given that USB is 5V?

Thanks!