A variety of problems—some rather subtle, or impossible to ignore—can indicate that the internal battery is swelling, such as the screen not closing properly, a gap between the upper and lower parts of the case(enclosure splitting), a failure to sit perfectly flat, system rocking when placed on an even surface, touchpad or keyboard lifting or not working properly, and keyboard and touchpad might begin to warp or could start protruding. Sometimes it may be accompanied by: overheating, fast-draining battery.
If your system has gone through 500-600 charge-discharge cycles, you should replace the battery on priority basis, some users who wait till the battery backup comes down to 5 minutes and don’t consider to replace the laptop battery then the battery can swell.
With an iPhone or iPad, a swollen battery is usually obvious because it starts to warp the case and can even crack the screen—it all depends on where the swelling takes place and what part of the device gives way first.
In some cases, a swollen battery may also leak, resulting in a very pungent strong smell of metal. This can easily damage other components to the point where it may be unable to be used.
If you smell burning or metal, it is best that you immediately stop all operations on your laptop and let it be looked at by a professional.