If it puffs up too much it could cause major problems, and could get stuck in the copter! You could use just for on the ground calibrations checked etc.
Is a swollen battery dangerous?
Simply put, yes. It is generally not recommended to continue using a swollen LiPo battery, although it is still possible to use a few more times until you get a replacement. Special care must be taken when charging a swollen LiPo battery. If possible, have it charged away from flammable materials or in a fire-proof container. A swollen LiPo battery is also particularly sensitive to mechanical failure of the casing, so avoid tampering or any type of impact that will pierce, dent or damage the battery.
If you really must, use that swollen LiPo battery, then go for it at your own risk. As long as you’re careful, it should be fine. However, you should be looking for a replacement as soon as your battery starts to show any swelling. It will only get worse over time, and you can only push your luck so much.
What causes a LiPo battery to swell?
To understand why a LiPo battery (or any other battery, for that matter) swells, we need to understand how its individual components interact to make the battery work. All batteries are made with three basic components: a negative end, a positive end, and an electrolyte solution. Batteries conduct electricity via the migration of ions from the positive end to the negative end and vice-versa. These ions can travel through the electrolyte solution.
LiPo batteries are distinct from the old-fashioned lithium-ion batteries due to their use of a solid polymer electrolyte. Through this solid electrolyte, lithium ions can move between the two terminals of a LiPo battery. A LiPo battery also has polymer separator that keeps the positive and negative terminals from coming into contact with each other.
Batteries swell because of the phenomenon of electrolyte decomposition. As its name implies, this is the process where the electrolyte solution decomposes into its individual components. In most cases, these components include oxygen. In the case of LiPo batteries, the polymeric nature of the electrolyte means that they also tend to produce carbon dioxide (CO2) and carbon monoxide (CO) when they decompose. The production of these gases is what causes a LiPo battery to expand and swell.
There have been a lot of instances of LiPo batteries catching fire while they are plugged in. The chances of a LiPo battery charging fire is even higher once electrolytic decomposition has kicked in, as the oxygen-rich gases are very flammable, A good practice to follow is once your LiPo battery has indicated that the battery is full, disconnect the battery and switch the charger off at the wall, and never leave the battery connected to the charger unattended.
One thing to remember about battery swelling is that it cannot be avoided. Electrolyte decomposition is a naturally occurring process, albeit it should be a slow one. However, improper maintenance of the battery can accelerate the decomposition process.
