MACBOOK A1398 820-00163-A No Boot

I have made a few tests as well , for instance if i disconnect the battery and plug charging cable it powers on , but then even with the original battery sometimes if i disconnect and connect the battery then connect the charger it would not even give him the orange light , so i have to connect it again without battery to get a boot then shut it down then it would give me a boot with the original old battery with the charger connected of course , but with the new battery connected i got nothing , no amber lights , no boot , Nothing at all.
I do not have another board , The battery that i got was from another computer but was shipped to me from California, so i do not have another board of the same type here, should i replace U7000 By a new one?
I did what you said , and this is what i came up with , U7100 was shorted, So I changed it and its charging , but sometimes it stops and i have to reconnect it again , I believe the magsafe connector also needs changing, I will inform the customer about that as well.
For instance , if it goes on sleep mode with magsafe charger connected , as soon as i press any key to wake it up , it would immediately stop charging then I have to disconnect and reconnect it again , if i type password to unlock device it does that too , what might've caused that kinda behaviour, and magsafe charger got very hot while charging.