Karbonn A52+ automatically turns off constantly

I'm using a Karbonn A52+ running Android 4.2.2. I have been facing a problem, many times, in fact, most of the times, when I'm using my phone, it automatically turns off (Not when the phone is not in use). Then when I try to switch it on immediately, it doesn't.. It switches on only if I try after a while. Sometimes it even requires the charging of the battery, even when it has a decent amount of charge remaining. Sometimes, even such a thing happens: Phone has 90% battery, it switches off, I reboot, it has 1% of battery. I take the battery out and reinsert, it again has 89-90%. I found an article on the net saying if the phone's testing mode says the battery is healthy (which I did confirm in my phone), most probably it is a software problem. I tried uninstalling recently installed apps, problem persisted I removed the SD card, phone worked fine for 10-15 minutes, again switched off Now when I run the phone WITH sd card, it goes off almost immediately after booting. I even tried disabling quick boot (which I don't remember when did I turn it on), problem persisted.. I went on and performed a factory reset, phone worked fine for a day (or perhaps less) and the problem started repeating.. So I'm unable to make out whether it's a software or hardware problem.. Shall I go ahead and flash my stock ROM or buy a new battery? P.S. I have once flashed my stock ROM due to a soft brick around a month or two back..