Is this a Battery issue?

[EL620]

I'm currently the owner of a new Lumia 822 from eBay for about 4 months now, but I noticed something strange about the battery life. The battery will function normally on light usage, but sometimes the device will show a random battery low warning at 9% in the action center especially when playing games like Asphalt 8 or GT Racing 2. This also happens frequently when the device heats up ( Screen and back area ). After plugging the charger in most cases, the battery percentage will return to where it was before the 9% drop.

So I was wondering if the problem is the battery or a software problem.
Flashing didn't solve the issue so I'm looking to get a new battery.

The Battery is a BP-4W 1800 mAh

 

[RumoredNow]

It does sound like the chip in the battery is defective...

 

[EL620]

It does sound like the chip in the battery is defective...

After looking carefully, i couldn't find any Nokia branding on it which means this could be a generic battery.