Automatic black screen in Inspiron 15 5570

When I power on my laptop it runs fine  for 20 mins or so then it shuts and blackscreen appear as if a power cut in cpu...

And I'm I'm not able to power on laptop as if the power button is disabled for at least 5 mins.

And when I try to power it on again it shows 3amber and 1 yellow .and goes into the bios and says time and date not set and when I go in bios and change boot sequence to internal HDD first and reset time and exit after that the computer boots after few minutes and then after 20 min this process continues.

And when I took diagnostic test by pressing F12 and selecting that option it runs and says your battery reached end of usable life .and also when I use the computer for those 15 to 20 mins the battery drowns very fast.

Dell technical call support said that I have to replace the mother board and that will cost 12000 rs around 200$ 

My battery health is  57%

And AC adapter shows 65W connected on bios battery settings and health status good  I'm frustrated.