You may find that when you recharge your battery it gives off a strange smell due to a release of sulphur dioxide. This generally indicates that your battery is being overcharged. If your battery is also hot to touch, it’s in danger of being damaged. As gas is being emitted there is a danger of fire or, in the worst-case scenario, an explosion, so it’s best to stop using it and have it checked over by a professional.
Also, make sure you don’t disconnect your battery from charging while it’s connected to the mains as this could cause a spark and trigger a fire.