LG G2 randomly shutting down. Battery issue?

[cu4t]

So about a month ago I purchased a second hand LG G2-D802 online and for the next three or so weeks it was working great. But just last week when I was using it, it randomly just shut down. I didn't think much of it at the time, plugged it into the charger and left it overnight. Then the next day I was using it as normal, checking emails, and it did the same thing again. I noticed that the battery was at about 70%-80% at the time it shut down. Then when I tried turning it on immediately after this happened, it would reach the home screen then immediately turn off again. It's as if the phone thinks the battery is at 0% charge, so it shuts itself down. It would only turn on again when I plugged it into a charge, where it would recognized that the battery is not at 0%. There is also no telling at what percentage the battery would shutdown, as it was varied ever time, but has happened sometime during every charge. Along with this, I've also seen abnormalities with the charging and discharging of the phone, where the phones battery would fully discharged in about 1 hour, and charge up at about the same rate, which can be seen in the linked images. This has continued to happen over the remained of the week and I've tried everything I could think of to fix it; factory reboot, re calibrate the battery, uninstalled or disabled battery draining apps, but nothing has helped. I also couldn't find anything online which has a similar issue to mine. Is it as simply as replacing the battery? Or is it something else? Any insight would be much appreciated. Unfortunately, I can't link you the images.

 

[Rukbat]

It sounds like a battery that's been mistreated and is at about the end of its life. Replacing it - and treating it properly - will probably cure the problems. (Don't let any lithium battery drop to below 40% charge - they don't last long with deep discharge. That one is 2-1/2 years old. I have one in an 11 year old phone that's still working fine. That's the difference between 40% minimum and draining the last ounce of power out of the battery on every charge cycle. Also, if it's too hot or too cold for you, it's too hot or too cold for the phone. Keep it near your body if you're in the cold outdoors, and protect it from direct sunlight if you're out in the summer. [And NEVER leave a phone in a closed car in the summer. You can destroy the electronics and the battery.])

 

[cu4t]

So here is an update...

I ended up purchasing the battery and replaced it in late February with a new genuine LG G2 battery. It had been working fine for about the following month, about the same time frame that the last battery lasted (even though that one was in the phone when I purchased it second hand), and now since about last week, the same issue has reappeared, where the phone randomly shuts down and wont turn on again unless its plugged into a charger. Therefor, I can only conclude that it must be a different component of the phone that is defective. I have noticed that the battery, after replacing it, no longer heated up like it used to. However, the back of the phone at the top (around the buttons) still continues to get surprisingly hot. Does anyone have any suggestions as to what the problem might be? I was thinking that the motherboard may be faulty. Any insight would be great thanks.