Two weeks ago while on a trip in the Philippines I was flying my Mavic Pro. I was out about a Kilometer when I got a low battery warning, so I let the Mavic return home. When it landed the battery was at six percent. When I took it out of the mavic it was quite swollen and had not been before. I thought maybe it happened because it was drained from the long flight. I put in another battery for some more flying. I landed with between 30 - 25 percent charge left. I removed the battery and it was a little swollen too. Never before. I flew my third battery and when removed from the drone it was not swollen at all. After cooling down the second battery returned to normal. No swelling. The first battery that was very swollen was not as swollen, but was still a little. I charged them all up and then did a battery status check on each in my Drone. They all charged up to 4.22 volts. I still get the same flight time from each battery between 18 and 20 minutes coming home with about 25 percent left on the battery charge. Now after each flight the two batteries are swollen, but the swelling subsides after cooling down. The first battery that was the most swollen is pushing agaist the battery locks after flights. When I squeeze the battery it feels like the swelling is air inside the battery. There is no squishing or hard resistance. It is strange to me that two batteries swelled within minutes of each other. I am sure that they were never swollen before, I would have noticed. The temperature was around 90 degrees and the Sun is very strong here. My Drone is hot to the touch after flights.
   Any thoughts on my battery stuation?

As faras I know, heat and humidity usually make a battery swell. They were operating outside parameters, either because of environmental conditions, their age and related state or a problem with the drone itself.

Buy a new battery and see how it goes , then replace the others or have the Mavic serviced. All cheaper than loosing the thing.

If you push your batteries hard on a hot day , or recharge while they are still warm they might swell. Apparently older batteries are susceptible to this as they age.

The danger is that the swelling may be enough to force the latches open and eject the battery in mid-flight - This has happened according to some previous posts on this forum.

If the problem persists then it's time for some new batteries, much cheaper than a new Mavic Pro

Swollen LiPo batteries are damaged and are dangerous to handle.  They should NEVER be recharged and should be disposed of properly.   Check out this link:
  http://learningrc.com/puffed-lipos/ or google "puffy lipo battery".

LIPO fires are a real deal mate. If you have a puffed up battery, don't recharge it or try to use it. It's not worth losing your drone or your house over a $80 battery.

Hello and good day rbtmckny. I am sorry to know about this trouble and thank you for reaching out. Battery swelling is basically caused by to much heat, vast changes in temperature and/or moisture getting into the battery itself. Batteries should be stored at a constant temperature of around 20 to 25c when not in use and kept away from direct sunlight, damp, water etc. In addition please do not fly your drone with swollen batteries this might lead to an accident during the flight. Finally I would recommend you contact our support team to start up a ticket: https://www.dji.com/support for us to help you further with this matter. Thank you.

By any chance were you flying in sport mode?

AG0N-Gary Posted at 5-11 16:21
By any chance were you flying in sport mode?

No, normal mode.

Recommend battery replacement.  Inflight swelling could lead to damage of the craft, or worse, damage to property and lose of craft.