My 2014 X8 originally came with two of the Tiger Power 6000 mAh 4S batteries, and I’ve probably gone through 24 cycles each on them. I purchased another battery from 3DR a couple of months ago, and it has only had 4 cycles so far.
Due to a personal injury on August 29th, I had not touched the X8, and the batteries had been left in the case, all at a full state of charge.
Yesterday, I pulled it out and checked the charge on them. The two older ones were at about 4.11V, and the cells still balanced within 0.1V of each other. The newer one had a higher state of charge, about 4.14, also balanced, but I noticed as soon as I pulled it out of the slot that it had swelled a bit.
I measured with a caliper, and while my old batteries are 41mm in height (including the velcro backing), the new one is now 45mm at the center. The bulge is squishy and feels almost like an air pocket.
I ran one of the old batteries and the new battery through test flights, and both drained fine. The flight took the new (bulgy) one down to 15.1V, and the old one down to 14.9V. Both were comfortably warm to the touch immediately after the flight and the swelling had not changed.
I left the new battery in my LiPo bag on the tile bathroom floor overnight with a fire extinguisher nearby just to be safe, but as I expected, it did not change in the slightest.
So. What is up with it!? Is this much swelling acceptable? Could it be defective? Could it possibly be due to sitting at a 16.6V full charge for three weeks? If so, why would it not affect the other two which were charged and stored identically?
I’ve always tried to be vigilant with my LiPos because I’ve heeded the warnings about them. This is my first experience with one swelling at all, so I’m hoping some of you with more experience can help me properly gauge my reaction.
-Daniel