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I have the following scenario:

I am testing several laptops with Windows 8.1 installed. One of the tests is to measure how much the battery lasts. For this task I use benchmarks like PeaceKeeper or PowerMark.

I also want to measure how long it takes for the battery to charge itself to 100% after it gets depleted. Any ideas on how to do that?

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If you do not want to use external tools, you could tap the power (pun intended) of WMI queries and WMI Eventing. Simple query to run from command line:

wmic path win32_battery get EstimatedChargeRemaining

will give you estimated charge. Now, to get repeated readings you could just put it in a timed loop, but there is a better (or fancier :-) way: register a battery event and a handler for it - here it is done in Powershell (start Powershell and paste/exec those two commands):

$action={get-wmiobject -computername localhost -Query "Select * from Win32_Battery"|% {write-host battery charge: ($_.EstimatedChargeRemaining) time:  $(get-date)}}

Register-WMIEvent -query "SELECT * FROM __InstanceModificationEvent WITHIN 10 WHERE TargetInstance ISA 'Win32_Battery'" -messageData "battery charge" -sourceIdentifier "battery" -action $action

This will produce a line of output at your Powershell console each time an event is raised. Here is the output from my laptop:

battery charge: 67 time: 2014-12-11 17:59:53
battery charge: 68 time: 2014-12-11 18:00:23
battery charge: 69 time: 2014-12-11 18:01:23
battery charge: 70 time: 2014-12-11 18:01:53
battery charge: 71 time: 2014-12-11 18:02:53
battery charge: 72 time: 2014-12-11 18:03:23
battery charge: 73 time: 2014-12-11 18:04:23
battery charge: 74 time: 2014-12-11 18:05:14
battery charge: 75 time: 2014-12-11 18:06:04
battery charge: 76 time: 2014-12-11 18:06:44

My simple action is just a console message, but you could of course do whatever you like - for example write it out to file

(note: I think WMI counter goes to 99 which is shown as 100%/full at the status bar - so it's 1% 'behind' the display)

  • That's a neat trick. WMI comes in handy for a lot of stuff. If only it were easy to learn. Are you aware of any good places to start learning about it? +1 to you. – Vinayak Dec 11 '14 at 19:47
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    @Vinayak MSDN has quite a lot of information, see here for examples: msdn.microsoft.com/en-us/library/aa394585%28v=vs.85%29.aspx Related so question: stackoverflow.com/questions/896188/… – wmz Dec 11 '14 at 21:52
  • When I run wmic path win32_battery get EstimatedChargeRemaining, I get 4 as the result. What does that mean? How do you interpret the results? – Corporate Geek Dec 15 '14 at 13:19
  • @CorporateGeek This should be percentage: EstimatedChargeRemaining Data type: uint16 Access type: Read-only Estimate of the percentage of full charge remaining (full class reference msdn.microsoft.com/en-us/library/aa394074%28v=vs.85%29.aspx) – wmz Dec 15 '14 at 13:26
  • Mmm... wmic path win32_battery get EstimatedChargeRemaining is not useful then. It tells me how much charge the battery has. I need to measure exactly how long it takes for a battery to charge from empty to 100%. – Corporate Geek Dec 15 '14 at 13:29
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Battery Eater supports creating a battery charging graph.

Battery Eater

It also logs the current battery capacity every 30 seconds during a discharge benchmark. I suppose it also logs this information while creating the charging graph.

Here's a snippet of the discharge log:

Log started: 13-01-2014 20:15:43
===============================================================================
[20:16:13]  36680   0
[20:16:43]  36630   0
[20:17:13]  36590   0
[20:17:43]  36530   0
[20:18:13]  36490   0
[20:18:43]  36430   0
[20:19:13]  36370   0
[20:19:43]  36320   0
[20:20:13]  36280   0
[20:20:43]  36220   0
[20:21:13]  36170   0
[20:21:43]  36110   0
...
[17:52:38]  2080    0
[17:53:08]  2250    0
[17:53:38]  2410    0
===============================================================================
Log ended: 14-01-2014 17:53:45

To open the BEG files it generates, drag-and-drop them into the Battery Eater executable file. Also, since this is pretty old software, you may need to run it in Compatibility mode.

  • Where is that BEG file generated? Where do you find it? – Corporate Geek Dec 15 '14 at 13:21
  • The BEG files are generated in the same folder as BEPro.exe. The folder names correspond to the current date, so if you did a benchmark today, they's be named 15_12_2014_1, 15_12_2014_2, 15_12_2014_3 etc. The BEG files are located inside these folders along with the log file. – Vinayak Dec 15 '14 at 15:36

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