Nexus 7 faulty mainborad or battery - not charging

My Asus Google Nexus 7 2013 LTE fell from my pocket and a car run over it. The body wasn't damaged but the LCD was broken and the touch screen was damaged. the tablet was on, and after that I was able to check that it was working by pressing the power and the volume buttons which responded properly.

I sent the tablet to LetMeRepairUK which is the official ASUS service center in the UK and I was expecting them to repair the tablet that apparently just need a new LCD and touch screen.

After more than 30 days, they sent me an email said the the tablet passed the final test and they will ship it in a couple of days. after a week, I contacted them and they said the the tablet failed to operate. and after couple of weeks they said that the tablet need a battery and mainboard replacement which will cost 250£ and I have already paid 240£ for handling cost and LCD so they refund me the whole money because the repair is not cost effective. And they sent the tablet back which was with a new screen.

I have recieved an email from the service center : "unit would not charge, we think it is not charging due to a faulty battery/mainboard, rather than just a charger. We tried a new power supply and the unit still did not charge." !!

Now, I have just received the tablet, and the screen is new, but it doesn't boot, when I link it to the computer the device "Qualcomm HS-USB QDLoader 9008 (COM5)" appears in the device manager.

what do you suggest?

Edit: I have tried to install a battery from my friend device (which is nexus 7 2013 wifi), my device worked and I tried to charge the battery and it worked, but the device is only booting to the safe mode.