Linux Laptop Battery Life Measurement Methods
Here we take a closer look at the methods available to observe and measure battery life , no matter vgp-bps9 battery or sony vgp-bps12 in a Linux context.
Using an AC Watt Meter
Consumer-grade Watt Meters with a resolution of 0.1Watt and 1-second sampling rate are available for about 100 US Dollars. 3 While intended to tell you the cost of operating your old refrigerator, they can just as easily tell you the A/C draw for a computer , dell vostro 1200 battery for example.
It is important to avoid the load of battery charging from this scenario by measuring. This can be done by measuring only when the battery is fully charged, or for laptops that allow it, running on A/C with the battery physically removed.
You’ll be able to see the difference between such steady-state operations as LCD on vs. off, LCD brightness, C-states and P-states. However,it will be very difficult to observe transient behavior with the low sampling rate.
Unfortunately, the A/C power will include the loss in the AC-to-DC power supply “brick”. While an”External Power Adapter” sporting an Energy Star logo 4 rated at 20 Watts or greater will be more than 75% efficient, others will not meet that criteria and that can significantly distort your measurement results.
So while this method is useful for some types of comparisons, it isn’t ideal for predicting battery life. This is because most laptops,also toshiba pa3399u-1bas and toshiba pa3399u-1brs , behave differently when running on DC battery vs. running on AC. For example, it is extremely common for laptops to enable deep C-states only on DC power and to disable them on AC power.
Using a DCWatt Meter on the DC converter
It is possible to modify the power adapter by inserting a precise high-wattage low-ohm resistor in series on the DC rail and measuring the voltage drop over this resistor to calculate the current, and thus Watts.
This measurement is on the DC side of the converter,and thus avoids the inaccuracy from ACDC conversion above. But this method suffers the same basic flaw as the AC meter method above, the laptop is running in AC mode, and that is simply different from DC mode.
Replacing the Battery with a DC power supply
The next most interesting method to measure battery consumption on a laptop is to pull apart，the battery and connect it to a lab-bench DC power supply.
This addresses the issue of the laptop runningin DC mode. However, few reading this paper will have the means to set up this supply, or the willingness to destroy their laptop battery,include mine vostro 1200 battery.
However, for those with access this type of test setup, including a high-speed data logger; DC consumption rates can be had in real-time, with never a wait for battery charging. Further, it is possible that system designers may choose to make the system run differently depending on battery capacity. For example,high-power P-states may be disabled when on low battery power – but these enhancements would be disabled when running on a DC power supply that emulates a fully charged battery.
Using a DC Watt Meter on an instrumented battery
Finally, it is possible to instrument the output of the battery itself. Like the DC power supply method above, this avoids the issues with the AC wattmeter and the instrumented power converter method in that the system is really running on DC. Further, this allows the system to adapt as the battery drains, just as it would in real use. But again, most people who want to measure power have neither a data logger, nor a soldering iron available.
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