I had situation where one of my batteries developed a slight (very slight) bulging on the upper and lower flat portions of the housing. It is so slight, that you really can only feel it when you compare 2 batteries side by side (one in each hand). I became a little worried and contacted Yuneec. It was under warranty, so they sent me a replacement. I had heard that Yuneec was rather slow on shipping out replacement parts, so I wasn't expecting it for several days. Come to find out the battery was delivered 5 days ago. I didn't find the package until today due to the ups driver placing something on top of the package to protect it from rain and I have been getting in late from work. Now the battery has been on my front porch (Central Florida) for 5 days straight. Since it was covered, it wasn't in direct sunlight, but it does get hot during the day. When I opened the package the battery was not hot, but was a little warm when I opened it. The new battery also has a slight (again very slight) bulge in the same location as the first one. Is this a normal circumstance for these batteries. Is there a way to test out a battery to find out if it is faulty? Have anyone else's batteries developed the slight bulge? If so, this would definitely allay my fears. It makes me very nervous that my drone could fall out of the sky due to a faulty battery.