lmao, this conversation is hilarious XD
Here is what you need to do: get the battery till around 20 per cent, then type in the dialer *#0228# at that point a screen with quick start written on it should pop up. Connect the phone to the charger and ONLY then press quick start.
Leave the device plugged till it has fully charged and do not use it, my advice is to put it into plane mode before doing this and to go back to it after 2 or 3 hours in order to turn the screen on only when it is at 100 per cent.
Once it reaches 100 per cent unplug it and exit from that screen (do not press quick start).
This procedure will calibrate the phone battery (it is a system tool to find back again how much charge can the phone hold) and by doing so you should not experience sudden discharges.
However note that if the phone keeps doing that you will need to have your battery replaced.
Also a quick tip I can give you is not to let the phone discharge fully and not let it go below 20 per cent, but charge it before. Running the battery to low charge levels (or even full charge/above 80 per cent) increases the reactions at the cathod and anode and reduces the life cycles of the battery.
Let us know if what I suggested solved the issue
tecnically charging the phone to 99 per cent does nothing compared to 100 per cent, since even when the phone shows 100 per cent in reality it is not fully charging the battery to protect it.
Also note that i you want to increase the lifespan of the battery due to the curve voltage-current of Ion batteries the most degradation of the batterie happen between 100 and 80 and between 20 and 0 per cent, so the optimal range to run your battery is between 80 and 20 (the ideal would be 60 and 30, but 80 and 20 is what has the most battery to use to lifespan improvement value)
What if I told you you always did it wrong?
Look at my message above, I gave a quick explanation regarding the ideal levels to run your battery at