From: legg@nospam.magma.ca   
      
   On Sun, 07 Dec 2025 08:09:04 +0000, Charlie+  wrote:   
      
   >On Sat, 06 Dec 2025 16:27:19 -0500, legg  wrote as   
   >underneath :   
   >   
   >>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.   
   >>   
   >>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.   
   >>   
   >A thing I found is that the permanantly attached buck or boost regulator   
   >in these batteries, (PP9 EBL with USB boost reg. in my case) can drain   
   >the LiPo well below ideal V either in storage or instruments that are   
   >only used occasionally, so worth keeping an eye on that type of very   
   >life shortening behaviour!   
   >I would suspect the 1.5v might follow the samee pattern except with a   
   >buck reg..  C+   
      
   In equipment designed for regular primary cells, the best you could   
   hope for was a low battery indicator, which usually gets ignored   
   until performance is visibly affected.   
      
   With rechargeable bodies employing who-knows-what inside the can,   
   things are different. You're counting on the internal BMS qualities   
   of the adopted internal interface circuitry.   
      
   For micro-dollar devices from multiple vendors, the results are going   
   to vary.   
      
   One of the most common occurences in application specific captive   
   battery protection interfaces is a discharge to below values required   
   for the protection system to maintain function. These may refuse to   
   start or to be recharged - into the trash bucket. Often this is   
   simply the result of a badly selected voltage monitoring chip, or   
   a poor understanding of the 'who's on first' logic created by the   
   interface to the charging and protection hardware with which the   
   voltage monitor is attached.   
      
   I've seen product that attempted to improve product life (where   
   previously the end user was allowed to discharge the lithium cell   
   to rubbish) by introduction of a voltage monitoring switch. A   
   considerable number (not all) of the resulting units protected   
   the battery at a level where the pre-existing recharging circuitry   
    lost it's function - an unspecified or untested feature of the   
   custom silicon involved.   
      
   This probably corrected in the next iteration, if there ever was one,   
   but I doubt the experience is shared between multiple designers.   
   Very likely it will be different designer, each time.   
      
   RL   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)