Hello,
I have four 4S 3000 mAh. 20C Zippy batteries.
Each one has been charged about 30 times always at less than 1C and discharged flying the pattern.

The average drain after the pattern was always less than 80% and the cells voltages after landing were always more than 3.7 Volts.
The ESC was set to accept no less than 3.0 Volts/cell under the load and never stopped the motor in about 120 pattern flights during the last and present year.

The temperature of the batteries never exceeded 45 deg.C ( 113 deg.F). I used the properly calibrated infrared termometer to measure this temperature.

I have noticed two weeks ago that three of the batteries started swelling. The swelling increased the height of these three batteries by about 0.2" total.
The fourth battery stayed flat, though. Since then, I have made 12 flights (three flying sessions), the swelling stayed 0.2" and the fourth battery remained not swollen.

The swelling subsides after about 30 minutes. After each flying session, I let the batteries rest for 1.5-2 hours and start charging them one by one, watching the IR numbers.
I am using the Revolectrix GT500 charger with balancer.

A moment ago I have finished charging all batteries. The battery #4 IR numbers were virtually identical to the IR numbers of swollen batteries: 2.4-3.6 mOhms per cell. Why wasn't the battery #4 swollen too?

Is the battery #4 simply "better" and what is the meaning of "better". If this battery is from a different production batch and has, accidentally, better polymer electrolyte, why are the IR numbers the same in all four batteries?

The batteries have been bought in June 2017.
 
Your opinions and suggestions are, as always, appreciated.

Happy Flying,
M

 


   

I think no one here is able to say with confidence what's wrong with your fourth pack 
Perhaps it came from another production run and therefore has slightly different electrolyte chemistry or electrode properties - chinese have never promised us with their production process consistency.

This season I'v been using three 2700mah 6S Zippy Compact lipos and all three has the same "swelled a little after flight" issue. Though they still perform well. I usually start charging them again at field just after 10 or 15 minutes after flight, no problem with that. Also all three packs have inner cells with slighly higher IR than outer from the day first.

Greetings,
Vitalis