Solved! Laptop turns off suddenly

[Somosaphiens]

I have a Lenovo G40-70, i5 4th gen, 12 GB RAM. After 3 months of use, it started turning off while on battery with no warning notification or sound. I can't even use it for 20 minutes max. The battery might read 50%-90% and suddenly is drained to 0% and turns off.
I don't think it shuts down, because when I plug in the charger and turn it on, the windows I opened before it turned off are always intact. The fan seems to be working fine too and I checked the charger with another laptop and it doesn't have a problem either.
Also, when I connect the charger and then it on, the battery is always about 20%-40% full. It only takes up to 30 minutes to fully charge it and when I lower the brightness, it only takes a few seconds.
I checked to see how the power changes(with low brightness) when I work with Unity and it read as follows;
100% - 6hr+
99% - 3hr+
98% - 5hr+
94% - 6hr+
And poof, it goes off.
Haven't checked the thermal paste yet, and it would be really embarrassing if it's only an issue with the battery ?.

Edit: even without using any app, it turns off at 89%. I don't have many background apps running either.

 

[Sidfawy]

try to change the battery if the problem still on so you maybe need to update bios if not so here you go the problem in battery

 

[webworkings]

It is likely the battery. They tend to act rather odd when they are going bad. Charging way faster than normal, and then dying when they say they still have a high percentage left.

This happens because when they start to hold less and less of a charge, they give false readings as if the parts that no longer hold a charge are still good. So, since you are actually accessing and using less of the capacity of the battery, it charges the smaller amount way faster. Personally I think they need to make software read them better and give correct data.