There are several possibilities why a battery can feel hot or heat up.
In case of an external short circuit: this can happen when the battery is short circuited i.e. in a purse, or in a drawer.
Perhaps the battery was stored somewhere together with other metallic equipment, in that case it can happen that the metal parts make a bridge between the plus and the minus pole of the battery. If this happens, the battery gets an external short circuit and will generate a lot of heat. When stored loose and in draws or purses or circumstances like this, it is advisable to keep the battery in a bag or separated so it cannot make contact with other metallic parts.
In case of an internal short circuit: this can occur when the battery got a severe shock i.e. has fallen down.
In this case it is possible that infernally there is created a short circuit due to the shock. The battery will have a high current discharge and will heat up. It is recommended to preserve the battery against strong shocks. In case of usage: This occurs when a battery is wrongly inserted in the battery box or there is a deformed terminal. Then there is also the possibility of a short circuit, forced charging and heating up the battery. In case there is only heating up, please remove the battery very carefully from the appliance and let it cool down before disposal. Do not reuse this battery after cooling down.