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I purchased a Phillips trimmer recently'ish. Plugged into the charger, it shuts off when it thinks the battery is charged. |
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Well... not "shuts off" : "stops charging" would be more accurate. |
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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. |
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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). |
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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. |
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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. |
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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. |
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