Sony xperia E4g battery problem fast draining and wont turn on

My Sony Xperia E4g wont charge battery!

 Let me tell you at start, it is not only your problem. Many owners of Sony Xperia have this problem and the worst thing is that it is factory fault.
 So what can you do about this. If you have nerves and some soldering skills I can help you to fix this situation and charge you battery.

 Before you start fixing your Sony Xperia let me tell you how I figure it out and what I did before I fix my own Xperia.
 Firs I search for help on internet but I only found that most owners have problem and there is nothing more to do about it cos it is factory fault.
 No help, no single answer and only answer you can find is to buy new battery but even then you may have this problem.

 So what do I do with Sony Xperia E4G? 

 I open my Sony and take out battery to do some testing. Visually my battery looks good and when I measure voltage I get only 3.6 V which is to low for phone.

 Next I did is test phone charging circuit and I read 4V on battery terminals, so charging circuit looks fine and phone supply power to the battery terminals.

 Another step I did is that I open battery to try to charge battery cell directly and avoid that electronic that is in battery. Everything tells me that this could be problem and for some reason this electronic wont work. So I just need to be sure that battery cell is OK.

 I start charging battery cell directly with 4.5V. After 2-3 hours I measure voltage on battery cell and it was 4V. That's looks good for start and I continue charging until battery reach 4.3V.

 So I put battery back and turn on the phone and I was surprised that phone shows me 100% battery power.

 Normally I test battery for few days and it seems to be OK, so charging is the main problem.

 Again phone or that electronic in battery refuse to charge battery cell so I start thinking on "how to fix" this.

Solved: Battery repair on Sony xperia E4G and charging normally 

 I read again and do some research but there was nothing to find on net. Then I got an idea to solider wires directly from USB terminal to battery cell. I was wondering will that damage phone but while this is my old phone I don't care a lot. And If  success I will write an article about it and help to someone maybe :)

 You can figure it out, I succeed and now I can charge my battery but there is a little catch.

 Since now my battery can be only charged directly because I crossover electronic that regulate charging. This means that I am only one who can control charging time and I must be careful to not overcharging battery.

 I'm glad if I help you.