From: ehsjr@verizon.net   
      
   On 2/24/2023 9:52 AM, vjp2.at@at.BioStrategist.dot.dot.com wrote:   
   >     Looking to identify the 4v battery used to backup settings on 1980   
   HP2621A   
   > CRT video display terminal.  I can't find the battery type online. Seems all   
   > the manuals are truncated at chapter 5. It is discontinued and I just want   
   > the specs. seems 4.2v Hg or 3.8v Li.   
   >   
   >   
      
   Here's a _general_ answer.   
      
   A setting holding backup battery does not need to supply   
   a lot of current.  I don't know what your device needs,   
   but it is likely very low, perhaps not measureable with a   
   dmm as it may draw current in pulses.   
      
   That said, there are plenty of lithium batteries you   
   can choose from, and small voltage boost converters   
   (look on ebay) you could use to boost to 4.2 volts.   
      
   You may not need exactly 4.2 volts - I have no idea   
   what your device needs, other than what you posted,   
   except that setting backup is almost always (always ?)   
   very low current.   
      
   Ok, assuming 4.2 volts, here's where we are, so far:   
   lithium===>boost circuit===>device   
      
   Now, you want to charge the battery.  Ebay has lithium   
   cell charger/protector circuits. Now your circuit looks   
   like this: (view in fixed font)   
   lithium=+=>boost circuit===>device   
            |   
   chg/pr==+   
      
   In case the view is "scrambled" you'll connect the   
   charge/protect (chg/pr in the diagram) to the same   
   battery terminals that the boost circuit connects   
   to.   
      
   Ok, that's the general idea - using lithium, lithium   
   charge/protection circuit and boost (or buck/boost)   
   converter.  You need to know what you're doing with   
   lithium batteries, how to protect them etc, and how   
   to properly connect to your 2621A.   
      
   Good luck.   
   Ed   
      
   --- SoupGate-Win32 v1.05   
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