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I came across the following when I was reading up about fully drained batteries in phones:

If the phone is OFF for a month, then it is probable that the battery has gone down to a point that the BMS has shut it down. The BMS won't allow you to charge the battery because, in its own assessment, the battery is dead. Best way to test this case is to have another same phone with a good battery (or just a new battery altogether), detach the cable from that and test on yours.

Referring to the above, do Android phones have their BMS as part of their bootloader or kernel? Or is it a part of the Power IC itself?

Are there any safety mechanisms related to booting up a device with fully drained batteries? If so, why?
(Came across something similar)

I've had difficulties with phones in the past after batteries have fully discharged - eg the Moto G5 had some battery protection "feature" that stopped it starting up if it thought the battery was fully discharged - it was a bit over sensitive so would sometimes assume the phone was fully discharged when it wasn't. Try leaving it on charge for 24 hours or so then holding down the power button for for at least 20 seconds with it still on charge.

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Battery Management System is a very broad term that covers battery charging /discharging/monitoring / power IC /responding to critical events like shutting down on low battery level / User Interface actions (increasing CPU speed when user touches screen - touch boost) and many other things.

  • Your first quote is only instance of management system where the battery voltage has fallen to a very low level, and a protection circuit kicks in and prevents further charging. This protection mechanism is mandatory

To prevent the battery from over-discharging, a control circuit cuts off the current path at about 2.20V/cell.

  • Booting up from a fully drained battery, is not permitted, since it would only further drain the battery. Booting consumes a lot of power and doing so on an already drained battery can lead to irreversible damage to the battery. And what's the point of booting up, if the device can't be used thereafter?

There are ways to overcome these problems but it is best left to qualified technicians to handle it. There are many questions on this site dealing with such situations.

As you would guess from the first paragraph, this being a complex system, it is dealt at a low level, meaning at a kernel level with proprietary hardware interfaces. Related Where are the battery capacity files located?

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  • Thanks a lot :) I have some questions, which it would be great if you could answer them in your answer. 1. In context to this, do our stock phone chargers feature a wake-up feature or “boost” to reactivate and recharge batteries that have fallen asleep? 2. I remember having one of my old Nokia phones kept idle and separated from its battery from almost more than 3 years, and it worked seamlessly when it put it back and charged the phone. Why didn't self-discharge affect in that case?
    – Gokul NC
    Jun 14, 2020 at 9:45
  • Please feel free to edit the question title/OP if it's very broad; something related to how self-discharging is handled by devices?. BTW related to the 2nd question above, I found this on Wiki: Li-ion rechargeable batteries have a self-discharge rate typically stated by manufacturers to be 1.5–2% per month
    – Gokul NC
    Jun 14, 2020 at 9:47
  • For the first comment Gokul 1. No, they don't have, never read or heard about it. Besides, they would like you to buy a new battery or device? 2. When it is separated from the device, my guess is that the self discharge is lower, since it doesn't need to be monitored by system. I can't say why your Nokia worked after 3 years. A few weeks ago I was able to charge and use a Bose Bluetooth headset after it was lying unused for 7 years! That was a pleasant shock //Next comment, wiki you quoted is in line with what Battery University also
    – beeshyams
    Jun 14, 2020 at 9:57
  • Says. Battery University adds more self discharge for to the protection circuit but then all these are broad guidelines and the specific characteristics can only be provided by battery manufacturers. Re:edit, it's OK, you only asked based on what you read, so I don't think it needs to be edited just because it turns out to be a broad idea, rather than a specific issue. Of course, you are welcome to edit!
    – beeshyams
    Jun 14, 2020 at 9:59
  • I got in touch with Bose service, had a detailed discussion - Bose products have a mechanism of automatically cutting off battery connections to the CPU or controller, if the device isn't used for a long time. Effectively, it is like taking out the battery from device - hence the discharge rate is very low (you go to a shop and buy even a two year old device, it's battery will about 40%, ideal for long storage). That's how I could use it after 7 years though the overall life had become very low //
    – beeshyams
    Jun 20, 2020 at 11:27

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