From: legg@nospam.magma.ca   
      
   On Sat, 6 Dec 2025 19:12:35 -0700, Don Y    
   wrote:   
      
   >On 12/6/2025 2:27 PM, legg wrote:   
   >> Rechargeable 1.5V lithium batteries are complicated animals.   
   >> Not a battery, as such, so don't rely on standard battery   
   >> chemistry descriptions to cover them.   
   >>   
   >>  From tested behaviour:   
   >>   
   >> There's a real 3.7V lithium cell inside there somewhere, with   
   >> a charging voltage of over 4V on the battery terminals.Open   
   >> circuit when charge is terminated internally.   
   >>   
   >> When it's not being charged, a switching regulator takes over   
   >> to produce 1.5V on the same terminals, drawing from the   
   >> lithium cell. This buck regulator is unstable when the battery   
   >> is not being used, so the battery terminal voltage jumps around   
   >> if you try to simply measure it.   
   >>   
   >> I wonder what this does to devices that count on the low noise   
   >> usually produced by simpler standard cells. Guess I'll find out   
   >> the hard way. Loaded, the voltage will stabilize, but then you've   
   >> got normal switching ripple and, supposedly, emc issues.   
   >   
   >What about devices that count on the internal series resistance to limit   
   >the current delivered to the load?   
   >   
   >I.e., does the lithium capacity JUST change the total amount of   
   >available charge?  Or, is it exploited to also change the VI   
   >characteristics of the source?   
      
   Given the wide range of configurations, you'd have to examine each   
   individually, to answer your concerns.   
   >   
   >> Nothing in the literature (?)- it's still the wild west as far as   
   >> battery products go, in the far east. Currently less than   
   >> US$1.50 per in low volume retail.   
   >>   
   >> I lucked into a bunch of rechargeable 9V (PP3) lithiums the other   
   >> day - furnished with a micro-usb port for charging. Same basic   
   >> idea, but with a boost regulator supplying the terminal voltage.   
   >   
   >What sort of usage patterns are you trying to address?  I think the   
   >only items, here, with 9V batteries are smoke detectors (and they   
   >are mains wired so the battery is an afterthought).   
   >   
   >Consumer "batteries" all seem to be headed to AAA and AA (with a few   
   >AAAA just to screw things up).   
      
   9V is hand-held test equipment. I see few that are multiple AA or AAAs   
   so far ~ which IS actually the topic.   
      
   Some AAA rechargeables actually include a micro-usb charging port -   
   but I see vendors phasing these out in favor of two terminals and   
   internal (active) diode wizardry.   
      
   RL   
      
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