Need CCTV DVR security system. Budget : ₹3000

Guys,

In year 2015, whole CCTV + 4channel dvr (LEXUS brand) was installed by a local CCTV shop for ₹20,000 with 1TB hdd. Now its been 3 year, suddenly its showing wrong time. After I set to correct time, whenever I restart the DVR it gives 3-4hr of difference. But Date-Month-Year always display correct.

I replaced coin shape battery 2 times, still facing the same problem. I called a mechanic and he said, DVR motherboard is corrupted, you need to buy a new DVR. Everything is working fine, only facing the issue of incorrect time, because of that it messing with footage recording time. Is there any way to solve this issue? Or should I buy a new DVR ?

I have no idea what is the specification of this DVR. It seems to be chinese (LEXUS). So according to my OLD camera which DVR should I buy online ?

Specification of camera

AHD 1080P COLOR CAMERA
SYSTEM:PAL 2.0MP
POWER: DC 12V
VIDEO OUTPUT: 1Vp-p75ohm

S/N: 201504270311

Which brand should I go for DVR ? In future can I upgrade camera to higher megapixel ? Which beand gives better after sale service?