What's so hard to do that? Why do we have to take the adapter out of the wall or of the laptop so that the battery stays preserved?
-- pashute, Dec 03 2019

All about battery soc https://batteryuniv...ure_state_of_charge
Measuring battery state of charge [RayfordSteele, Dec 04 2019]

I purchased a Phillips trimmer recently'ish. Plugged into the charger, it shuts off when it thinks the battery is charged.

Well... not "shuts off" : "stops charging" would be more accurate.

What actually happens is the battery then starts discharging through the transformer. So, after a few days of being plugged in... it's mostly discharged.
-- FlyingToaster, Dec 03 2019


What is it about trimmers/razors that they can't get the battery management right?
I've had 2 Remington rechargeable razors. The first had 5 LEDs to indicate battery level. A couple of shaves would get it down to the final red LED... after which I could still get 3 or 4 shaves before it actually needed recharging.
The second had a 2-digit countdown; showed 60 minutes fully charged, & I can normally get another 2 or 3 shaves out of it when it says "Lo". However, occasionally the countdown will tick off the minutes at a much higher rate, about 1 minute (on the counter) every 3 seconds or so. Once it gets to "Lo", I can get 5 or 6 shaves before recharging.
I have told Remington about these issues, but they don't seem to care (ugh, on-line "Contact Us" pages that never get replies... ANOTHER thing I have a lot of trouble with).

Er, end rant...
-- neutrinos_shadow, Dec 03 2019


From my battery class 10 or so years ago, predicting battery state of charge is actually not terribly easy, based on just voltage readings. Battery voltage curves are variable depending on how frequently and how low they’ve been drained, limited by the chemical byproducts and anode and cathode shapes that accumulate over time. Usually they settle for approximations that read voltage but don’t bother with the amperage dip under load, so they pick an average conservative value that roughly correlates. The trick is that batteries are all a bit unique, and lithium has a very flat voltage curve compared to its % state of charge, so a small difference in voltage may indicate a large change in the state of charge, and being just a little off can result in large errors.
-- RayfordSteele, Dec 04 2019


All modern devices that aren't incredibly cheap do stop trying to charge the battery once it's full. For lithium–ion, charging usually ends at 4.2 V, and charging from 95% to 100% is usually done at a very low rate compared to the rest of the charge.

What causes battery degradation in some plugged-in laptops (Mac laptops, maybe others) is that the laptop, when its power demands exceed what the power adapter can supply, will pull energy from its battery for a bit, until the power demands are lower, when it will recharge the battery. You, the user, will not see that this is happening, but it does damage the battery over time.
-- notexactly, Dec 04 2019



random, halfbakery