My Xiaomi Redmi 5 Plus is dead, won't charge, LED is blinking.

@moogibettoid first make sure that you let the battery fully charge. Once you know you have a fully charged battery, give it another try. If the results are the same, you do want to check the charging board. Make sure that you have the proper voltages going into the phone. I would even suggest that you consider replacing that board, just to rule it out as a cause for this. Since ifixit does not yet have a guide for that, use teh one from here It was written in Spanish so use a browser that will translate it for you, if needed.

Check the flex cable from the charging board to the main board. Make sure there are no tears, corrosion on the cable and the connectors.

If all of that is working properly and you verified that it is, then the issue can be related to the charging circuitry on your motherboard. You could check it against images like this

This is NOT an endorsement for the original poster of this image. It is only for illustration purpose.

and then measure the components according to the schematics. You could also check the test points around the battery connector and see what you get on those. Never an easy repair but there are always options. Of course, if this is above your skills or tools you need, you could consider finding someone who can do this for you. Going to be expensive :-)

Here are the Redmi 5 Plus Charging Schematic and here is the Component Layout to locate the components on your board.

One other thing. Do not forget to ensure that your software is properly installed etc. Faulty software can/will also interfere with regular operations like charging etc. You should always consider a factory reset, for as long as you have the original account information that you used when you first set up the phone. You will need it to gain access to your phone when you do perform a reset. Also, you will lose your music/pictures/SMS/contacts etc. from your phone. Let's hope you've backed that all up.