My Huawei mobile phone will be fully charged and then show battery flat and turn off. When turned back on it shows it as 60% or so charge and then turns off again .
It's called a dendrite in the battery. (You can read about it in these articles - Lithium Battery Dendrite links.) It's a big problem, but it's not solved yet. So, as jasonandrews said, you need a new battery.