Default [Q] Discovery V5 troubleshoot

I need help with the phone. I have discovery V5, android 4.2.2 Z3Z6Z7W MAUI.11AMD.W11.50.SP....... etc phone where battery life is no longer then 3 hours on standby. I have received 2 batteries and both of them have same life expectancy. When I contacted supplier I bought it from, they agreed to send another battery, but the problem is same even with the 3rd battery. So, I am guessing issue is with the phone but I am hoping it is something to do with the system and it could be fixed with some kind of update. I am not an expert in those things but being into elecltronics for more then 20 yrs, I do have some kind of knowledge, but not enough in this sphere.

Any ideas what could i do and how, please ?