I have 2 batteries Turnigy 5000mAh 4S 40C Lipo Pack that I got from HobbyKing about 6 months ago, but only in the last 2-3 months I started to use them about 3 to 4 times per week. Before that I kept them at 50% storage voltage most of the time. I have a DJI F500 Hexacopter, with motors NTM Prop Drive Series 28-26A 1200kv / 286w, I get about 8 minutes of flight time on it, and finally, to monitor the voltage I got a 2-8S Cell Checker with Low Voltage Alarm (I got the one without the case, but can't find the link to it right now), the alarm is set to 3.5 volts, and I usually land within 20 seconds from when I hear the alarm beeping constantly (when the battery gets close to discharged I hear a single beep once in a while, depending on throttle)
The charger I use to charge them: HobbyKing 4B6 Balance Charger Plus Accessories (200W)
Because the charger is 50Watts per channel, it's charging at max 3.4 Amps, and it takes about 2 hours to charge and balance (and I balance EVERY TIME)
I usually wait 30 mins to an hour to charge them again after use (so that they are already charged for the next day)
I did not keep track of how many times I charged them, but I guess it is ~ 40 times
Today I went to fly my hexa, when I was done, both batteries are a little bit warm (as usual), and I noticed it's a little bit puffed. I thought the puffying will go away, but when I got home after 2-3 hours, it is still puffed a little bit, and the total voltage (after 2-3 hours of sitting) is 14.8 Volts.
So here are my questions:
Will the puffing go away in time?
Should I charge the battery? Can I still use them? (is it safe?) does the puffing go away after I charge maybe?
What should I do? should I get new batteries? or different batteries? (with higher C rating?)
What am I doing wrong? (how should I prolong the battery life?)
Also... How do I know when the battery is about to blow? how much puffiness has to be? what are the symptoms? does it get hot before it explodes?