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Modern laptops come with the facility of being used in a plugged in mode only, without overcharging the battery. So, in such a case, the power consumption through the adapter should vary according to the workloads being run on the laptop.

How to measure this, so as to know what wattage of power is consumed during the periods of low usage vs intensive usage?

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  • To accompany @John's answer, wattage is determined by Ohm's Law: V[olts] x A[mps] = W[atts] (V*A=W) (Voltage is often represented by P[ressure] or E[nergy] in formulas in lieu of V; voltage is pressure, amperage is the amount of pressure, and wattage is the amount of power)
    – JW0914
    Commented Oct 26, 2021 at 11:55

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You need a Wattmeter to measure AC Adapter current under varying conditions.

There are reasonably economical wattmeters available.

Battery threshold is normally 80% (versus fully charged), so at 80 or 100% charge, the AC Adapter current draw will be about the same, and will be related more to computer load.

A wattmeter can help you here.

It will show average levels more than instantaneous levels, depending on the dampening within the meter. You may want a meter with a low power range to see your power level more clearly (a 100 watt Wattmeter won't show you much).

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  • I don't think this can be measured in any way. Power drained by the battery will be charged by the adapter at the same time, so either the adapter charges the battery and uses the rest for the system, or it uses the same power for the system and not charge the battery.
    – LPChip
    Commented Oct 26, 2021 at 11:55
  • A wattmeter will give a measure of average charge power. Because of the battery, it will not be instantaneous but the wattmeter will likely show battery charge power is the same at 80 and 100% when the machine is at normal idle.
    – anon
    Commented Oct 26, 2021 at 12:50
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If you use the computer while the battery is charging, the battery provides a bit of charge to the computer, and the charger charges the battery.

If the battery is not charged and the charger only powers the computer, then the charge that was initially sent to the battery is sent to the laptop instead. By that reasoning, measuring the power consumption will not tell you if the battery is being drained or not.

Therefor, the best way to know if your battery is being used or the charger is being used, is by running power intensive tasks and see if the battery drains or not, and compare this to running the same task with battery removed if you have that option (only to test, not a permanent solution). Also compare to the same task of only running on battery power to see how much slow down you experience.

This should tell you if your battery drains and gets charged, if it keeps charging to 100% or what else happens.

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  • It's generally not recommended to run laptops without their batteries since a battery's secondary purpose is to serve as a reservoir to absorb voltage and current fluctuations (this is the same reason why a vehicle should never have its battery disconnected while the engine is running - while the battery's main purpose is to provide enough current to turn the crankshaft, it's secondary purpose is to absorb voltage and current fluctuations from the alternator)
    – JW0914
    Commented Oct 26, 2021 at 12:06
  • @JW0914 oh, I agree, but for the same sake, its never a case where you cannot do this just to test something. In worst case, the laptop may crash, but if you are not doing anything that you could loose data with, its okay. But yeah, its a good idea to clarify that this is only to test.
    – LPChip
    Commented Oct 26, 2021 at 12:14

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