Okay well I'm going to follow up with some questions....
When you say:
it either shows low battery (on a full charge) or turns off suddenly.
How exactly do you know it's on a full charge if it shows a low battery then shuts off? What's the logic in believing it's fully charged? You just pulled it off the charger?
After some minutes wait it might or might not boot again.
If the battery is drained, I'm not surprised you can't reboot - even immediately. While it might boot a few seconds later, it will just shut down again and all the while you're doing more damage to the battery.
It does however boot again if connected to the charger.
As it should. If it's plugged in to the charger and getting power then it will start up.
This seem to coincide with the OS update.
What OS update?
I did a master reset but no change.
Okay so you did try a reset [sorry I missed that part when I wrote by initial post]. Did it continue showing these symptoms immediately or only after some time? [after installing apps and using it for a while]
"It turned of in the middle of a call for the first time, could not reboot it.Then I hooked it up to the charger and it booted showing almost no battery charge.I immediately restarted it again and the battery showed full charge."
If the battery is drained then it would shut down. When you restarted it the first time and it showed no battery, why did you restart it a second time [when it showed a full battery]? I'm not sure I'm buying that.
If the battery is drained, charge it up. If it shows a full battery and quickly drains in a matter of minutes or hours and you're sure you have no rogue apps then the battery is either defective or, through your method of charging / discharging it died. In either case, buy a new battery. Since it's been 15 months since you got the phone, I'm betting the battery is toast.
Thanks manik,I got a new battery and the problem is solved.On the old battery (15 months old) the phone would shut down on a full charge unpredictably in the middle of a tasked like working in a program, phone call ect..I could only restart it then by putting it on a charger (home or car).Then it would show battery almost empty,then I would immediately restart it again and the phone would show full battery again and would work till the next incident.