Unhappy Nexus 4 loss signal at low battery

Hi at all. Please help me I'm desperate.

I bought my Nexus 4 a years ago.

A month ago I noticed the problem of the red led of death and after that my battery drains very fast, but works normally (no issues of sudden drain).

Now my phone loses the signal every times the battery drains below 40% and I don't know why.

I tried to flash radio .48 from 4.2.2 factory image but it doesn't work.
I've also tried to change the preferred network from WCDMA preffered to WCDMA only, but nothing.

PLEASE HELP ME I LOVE THIS PHONE

P.S. In the last two weeks I have also changed mobile operator
P.P.S. Sorry for bad english