You can skip the story part but for better reference, please read it:
A Little Story
My phone claims it has a battery of 4000 mAh that lasts for 3 days. I got the phone, really psyched because of the battery. When I bought it it has 50% left on the battery. I did some texts and some first time testing on the phone, but no heavy usage. The phone lasted 19 hours before saying it was now low on battery (5%).
The next day, I charged it for six hours, turned on the 3G and used the Facebook app, Opera Mini, and Google Play for four hours before I removed the 3G. The battery read 29%. I was disappointed. Most of the people who bought this phone reported that it should last 10 hours with 3G on and heavy usage. Most people even say that with heavy usage their phone lasts 2 days, using the internet, apps that require it, and gaming with the phone.
Now I'm on the process of claiming the warranty and I called some service centers to determine where I will take it to. The first service center claimed that all Android phones last for only one day, the second one claimed that even if only a Messaging app is on, if I leave it open even if my screen is off the battery will be drained quickly. The third one basically told me to go to the Play Store and download a Task Killer. The last one I called told me to bring the phone to the service center so they could "observe it". That doesn't sound good to me.
My question is can technicians actually tell if the battery has the capacity it claims it has and if the battery is healthy? I want to go prepared to that service center if the observation they'll be doing will be to look at my "Battery" setting only and asking me what I've been doing only for them to say that's what been draining my battery.
Also can 3G drain a battery within 4 hours if a battery has 4000 mAh?
Note: My phone is a rebranded Innos D9, it's a Cloudfone Thrill 430x.