see the battery monitor and see which app during that duration of drain is using the most power.

then check the settings for the program such as sync and gps which are usually the culprits of battery drain. also check on googleplay other user comments about the battery life of the app whether they are also having the same issues.

i saw a few batter monitoring apps but i too am still unsure which is the best/accurate 
For example this betterbatterystats app
https://play.google.com/store/apps/details?...e=search_result

during charging ? thats very weird ....

were you using the phone while it was charging by any chance ? 

if you got usb3 ports you could try siyah's kernel that has this feature