Default [Q] G2 Korean Battery life

Hi I have G2 Korean version with removable 2600mah battery which is lower than the int'l version with 3000mah. I've use it for 2 months now until last week when it's the first time I forget to unplug it before I sleep so it was charged overnight. Then at noon time, the phone suddenly shut down with very thin lines. So I quickly charge it but there is a blinking red light. After an hour of plugging and out, thankfully, it charged properly but now I'm only getting 12 hours battery on light usage. I've heared that the non-removable 3000mah gets 19 hours battery, is this true? What's the normal battery life of the 2600mah? Should I get 16 hours (2600mahx19hr/3000mah)?

Did something gone wrong? Any recommendations? I still have warranty. I tried calibrating my battery by draining in and charging it fully while off , calibrating by software (Battery HD) and charging after 30 mins of usage of a fully charge battery (jump starting). Please note that same thing happened on the other battery which also charged overnight on the external charger pack.