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I'm using my laptop at home with battery removed and only connected to the AC power. However I'm lacking the mobility as my power cord is kinda short. Is it safe from electrical point of view to plug in the battery while the laptop is connected to AC and disconnect the AC power afterwards?

What about the opposite side of the question - is it safe (or what the damage could be) if you work on battery, plug in the AC and unplug the battery?

If there are differents for different models of laptops, I'm asking about IBM Lenovo T60. Is there such thing as a 'hot-plug battery'?

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6 Answers 6

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Most laptops have hot-plug batteries, which allows you to go to line power for a few moments so that you can swap out your nearly-dead battery for your fully-charged spare. I see Lenovos as being no exception to this.

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    Just in addition to this, you can use AC as your main power on the laptop as well, not just for a few moments, although the OP has already figured that out :).
    – Azz
    Sep 27, 2010 at 6:08
  • @Azz: That depends on the laptop. Many Thinkpads, for example, cannot do this because they cannot supply the surge of power the CPU needs when it comes out of a halt state without the battery. Oct 8, 2011 at 6:07
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I have a lenovo e545 that would not charge while plugged in. I looked around for every possible remedy for this and nothing worked. What did work was turning it on without that battery and then slamming the battery in. Now it is charging. HTH

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  • Sounds like either your AC adapter or the charging circuit in the laptop is defective. Apr 30, 2015 at 8:43
  • Were you able to figure out the culprit? Is it the laptop circuit or the adapter? I have exactly the same symptoms: 1) start on battery, plug adapter in - no charging, 2) start without battery, with charger plugged - laptop works 3) when laptop is working without the battery, swap the battery in - it charges 4) when the battery is charging, unplug the adapter and plug it in - no charging again. I also tried with various batteries - same result.
    – sd1074
    Apr 26, 2018 at 18:46
  • I found out that when battery is in and then the adapter is plugged, the adapter shuts off (output voltage gradually drops to 0), and the only way to restart it is to unplug it from AC power and plug it in again.
    – sd1074
    Apr 26, 2018 at 18:47
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Personally I wouldn't risk it. If, as you say, the power cord is short there's a good chance it'll come out during the operation anyway.

Laptop batteries are designed to be left in whilst the unit is on mains power anyway so you're not really gaining anything by removing the battery unless you're not going to be using the battery for an extended period.

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    Removing the battery may lengthen its life. If you remove it after decharging, then it will last longer than if it is always fully charged.
    – petersohn
    Apr 16, 2010 at 14:54
  • @petersohn - I've updated the last sentence to clarify it (hopefully)
    – ChrisF
    Apr 16, 2010 at 15:20
  • Li-Ion batteries have a lifespan of about 1-2k cycles. I know it is probably not worth it, but I'm trying to save a few cycles. And I do really need a battery at weekends when I'm travelling. Apr 16, 2010 at 16:47
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    Li-Ion batteries care less about cycles than simply about time and temperature. If you have a T60, then temperature isn't a problem since the battery is away from everything that generates heat on purpose (I see the same with my R60 and my Dell laptop). That being said, I have never seen a laptop battery die because of fiddling with it while the power cord was plugged in. I highly doubt there will be any effect at all; there's pretty much of electronics in the way to ensure various things.
    – Joey
    Apr 16, 2010 at 17:01
  • Can confirm this works with a Lenovo T540p just Googled this up to be sure before I slapped the battery in.
    – Arthur Kay
    Aug 10, 2015 at 17:13
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Insofar as I have successfully tried on different models of a Dell, an Acer and a Gateway, both old (down to 2007), and brand new - I haven't noticed any problem with hot-swapping batteries.

Just a note, even though I'm guilty for doing it I don't know if there's any use to take out a battery after it has been discharged to save cycles since I've read that only applies to older batteries; therefore, you will only want to hot-swap when you're actually hot-swapping 2 batteries and not just taking one out.

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My experience is just the opposite that of gregalabama. I have blown the charging circuit in two Thinkpads by hot plugging in battery packs while connected to AC and turned on. The models are a X41 and recently a X230. The laptops will run on battery power, but will no longer charge the battery. I know the battery is not at fault, because it will charge in another laptop of the same model. I think it may have blown one of the surface mount fuses on the main board. The X230 gives an error message that it is connected to AC, but will not charge and the battery should be replaced. But another battery gives the same symptom and error message, and both batteries will charge in another X230.

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No, you can't change batteries while the laptop is plugged in. Follow these steps:

  1. Turn the laptop off or put it in Hibernate mode
  2. Unplug the AC adapter from the wall
  3. Unplug the AC adapter from the computer
  4. Unplug any other wires connected to the laptop
  5. Remove or connect your battery

If you don't follow these steps, you could be injured.

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  • "...you could be injured." NO, YOU CAN'T. This "answer" assumes that 24 volts or less (which is the maximum voltage on exposed contacts on any laptop's battery terminals, power adapter output, or any other connector on a laptop) can be considered dangerous. This is flatly WRONG. 30 volts is considered the upper limit for "low voltage" (with which accidental contact is not a problem and therefore need not be guarded against) - see allaboutcircuits.com/vol_1/chpt_3/4.html . May 3, 2015 at 20:55
  • This "answer" also proposes a number of steps that would be completely unnecessary even if the charger output, or the voltage at the battery terminals, was hazardous. It's ridiculous. It's like saying you should turn a lamp's switch off, AND pull the breaker on the circuit, as well as unplugging it from the wall before changing the bulb. I can't decide if the writer was honestly overly fearful of electric shock or was having fun with us, but either way, this "answer" should be ignored with extreme prejudice. May 3, 2015 at 20:58

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