To check your battery detailed information, use next steps:
1. Start CMD.exe as administrator. (Click START button, type “cmd” and then right click on cmd.exe, choose Run as Administrator)
2. Type %cd userprofile%/Desktop. You can choose other destination where your raport will be created.
3. Type powercfg -energy
System will trace your system about one minut. After that, one HTML raport will be generated.
In this raport you can find many information about batery and power system. Most important can be battery capacity.
Next picture is example of raport section about internal and external batteries.