Template:Battery Testing

Understanding Laptop Batteries

The rechargeable batteries that power today's laptops are much more complex than the batteries typically found in other consumer electronic devices. They use sophisticated chemistry and control circuitry to maximize their runtime and longevity across years of use and potentially hundreds of charge/discharge cycles. Understanding their behavior - especially ones that have seen significant use - can be difficult but is very important for our Laptop Build processes. This guide is intended to help you measure and interpret a battery's vital signs and determine how much useful capacity remains.

Checking the State of a Battery
☐ To check and monitor the state of the battery, open a terminal and type:

watch -n3 -d cat /proc/acpi/battery/*/*

• The window should now display many lines of information about the battery that refresh every 3 seconds or so. The most important lines to look for are shown below with values taken from a healthy battery as an example. Other lines have been intentionally left out of this example and replaced with a -, but will appear in real-world use. Real-world values may be significantly different, use different units, or missing entirely.

Example

design capacity:       5200 mAh
last full capacity:    4331 mAh     
-
design voltage:        11100 mV
-
charging state:        charging
present rate:          1549 mA
remaining capacity:    3679 mAh
present voltage:       12358 mV

Battery Capacity
In this example we can see from the difference between the last full capacity and design capacity that the battery has seen some use but still has about 83% of its original capacity. If the last full capacity is less than 30% of the design capacity, the battery may end up being too worn out to function correctly.
Charging
We can also see from the charging state and present rate that it is charging at a healthy rate, and we would expect the value for remaining capacity to increase steadily until it is at or near the value for last full capacity. A battery will typically charge slower and slower as it approaches its last full capacity; when it is fully charged the charging state should change to charged and the present rate should be at or very near 0 mA.
Battery Voltage
You may also have noticed that the present voltage is actually somewhat higher than the design voltage; this is normal for a healthy battery, and when the battery is discharging the value will drop initially then settle in around or a bit below its design voltage. If a battery has

Battery Charging and Testing

Confirm the Battery is Fully Charged
☐ Set the laptop on the testing shelf and make sure it is plugged in to a power outlet.
☐ To monitor the state of the battery, open a terminal and type:

watch -n3 -d cat /proc/acpi/battery/*/*

• If the battery seems like it is healthy and charging normally, check the Start box next to Battery Charge on the Keeper Label and let it finish charging.
  

Test Battery Life
☐ When the battery is fully charged, open a terminal and run the following command:

batterytest

• Open a second Terminal (hint: press Super + T to quickly open a new terminal window) and run:

while : ; do stress-test ; sleep 300 ; done

☐ Disconnect the AC adapter from the power outlet, but keep it with the laptop for later.

How it works
The laptop will run the stress-test in a loop until it runs out of power. For every minute the laptop is on during battery testing, a line of text is logged in a file called bat_mon. When battery test is run again, the script counts up the number of lines of text in the bat_mon file, and outputs the number as the number of minutes the battery lasted.