My quest started with wanting to know if it is ok to keep phone plugged in. I've read https://www.quora.com/Is-it-true-that-using-your-smartphone-while-charging-it-destroy-your-battery-power-over-the-long-term and https://www.quora.com/What-happens-if-we-charge-our-mobile-continuously-for-a-week and there most people tell it is good for battery because phone just draws power from USB / charger (only some power hungry use battery power in addition to charger). However, only some phones can be used without a battery https://www.quora.com/How-do-I-use-a-smartphone-directly-without-a-battery. It is a problem for some dissussed here: Building a circuit to replicate a LiPo battery

I have several phones (one ~5 years old, other ~4 years old) with removable batteries and they do not work without battery. I have several laptops - all work without battery.

I recall laptops used battery to work even when plugged in, but it was many (like ~20) years ago. If as claimed by answers in Quora smartphones draw power from charger to work, why many phones do not work without batteries?

  • 3
    \$\begingroup\$ Are you asking how this is implemented technically? Or are you looking for why this is done? Because obviously it is technically possible to have it run while plugged in without a battery. \$\endgroup\$
    – DKNguyen
    Sep 5, 2021 at 0:31
  • \$\begingroup\$ Search on: lithium battery inflation. With Samsung and other tablets, it's recommended to NOT leave them continuously in the charger, since this gradually overcharges and destroys the battery (over years.) Probably this applies to some (all?) smartphones. Solution: replace battery with large-value capacitor, so the phone's "battery good" test-algorithm won't fail \$\endgroup\$
    – wbeaty
    Sep 5, 2021 at 1:28
  • \$\begingroup\$ @DKNguyen, I think I'm interested in WHY assuming there are technical reasons for difference laptops - smartphones, not only economico-marketing. \$\endgroup\$ Sep 5, 2021 at 2:52
  • \$\begingroup\$ @Martian2020 I don't have an answer personally unless it involves nefarious reasons or that the charger circuitry is just extra careful and does not let power through if it detects nothing on the output and no one bothered to do anything to change it. \$\endgroup\$
    – DKNguyen
    Sep 5, 2021 at 17:21

1 Answer 1


It's about peak power draw.

Over in the DIY stack we talk all the time about a large battery/solar system vs a generator. If you want to run dryer and water heater at the same time (10,000W between them), a 5000W generator cannot carry that load. But if the house has a battery system like a PowerWall capable of sustaining those loads for an hour or two, then the generator can handle the load, because it's borrowing the deficit from the battery, and giving it back after the appliances have finished.

Your phone is doing exactly the same thing. The phone has things to do, and it will do them even if their draw is >5W.

That can easily happen with CPU/VPU usage (3D games; Retina display)... or the display on "bright"... or cellular transmission in poor coverage areas.

Your core assumption is that every device is sized so its AC wall adapter can supply all the power it will ever use. That is not the case with phones and tablets, and that's partly because they charge from USB, and you never know what a particular USB port will be able to offer.

  • I've had to use tablets in bright sun, with the brightness to max, while plugged into a 5W USB block. The tablet was backsliding on battery life as I used it.

  • I've had phones that worked great in urban areas on 3/4G networks, but when you got out in the sticks with 2G, the phone consumed an inordinate amount of power. Even plugged in, it would backslide to 0 mid-conversation.

  • \$\begingroup\$ I see. One of my concerns was whether it is good for battery to leave phone plugged in for prolong time (weeks). From your answer fast charging ability is good in that scenario cause phone (hopefully) won't use battery (as opposed to low voltage charging) at all, correct? \$\endgroup\$ Sep 6, 2021 at 4:37
  • \$\begingroup\$ I can't tell you anything about that myth that it destroys batteries to leave them on charger 24x7. Because I don't believe that myth. But if you do, get an Intermatic clock timer that interrupts power 4 hours a day, so the battery gets some exercise lol. \$\endgroup\$ Sep 6, 2021 at 18:22
  • \$\begingroup\$ Myth, maybe. Here I've cited in the question (electronics.stackexchange.com/questions/450090/…) "We have already tested leaving the phone plugged in "stock configuration" and seen batteries swelling after about 4 months, which is not good." and wanted to build dummy battery, maybe phone tasks were not energy-intensive so they thought no need for extra energy supply. \$\endgroup\$ Sep 6, 2021 at 18:58
  • \$\begingroup\$ @Martian2020 note the model of that phone... the issue there is cheap Chinese. Maker either lacks the competence, or refuses to spend 2 cents extra per phone to do it right. \$\endgroup\$ Sep 6, 2021 at 19:38
  • \$\begingroup\$ There are also planned obsolescence efforts on the market as far as I understand (maybe not for that particular "feature"). Do you know what is most practical easy way to tell which phones "have it right"? \$\endgroup\$ Sep 7, 2021 at 2:37

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